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Husain M, Albalawi H, Al Huwayz M, Khan R, Rahman N. First-principle computation of some physical properties of half-Heusler compounds for possible thermoelectric applications. RSC Adv 2023; 13:23716-23727. [PMID: 37555085 PMCID: PMC10405639 DOI: 10.1039/d3ra04192a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 08/02/2023] [Indexed: 08/10/2023] Open
Abstract
Using the density functional theory (DFT) method, we investigate the properties of LaXSi (X = Pt, Pd) half-Heusler compounds. To ensure the stability of both compounds, we employed two criteria: the Birch-Murnaghan equation of state and the negative formation energy. The evaluation of elastic constants (ECs) plays a crucial role in determining the mechanical stability of both compounds. Specifically, we ensure that the conditions C11 - C12 > 0, C11 > 0, C11 + 2C12 > 0, and B > 0 are satisfied and exhibit mechanical anisotropy and ductility. The analysis of electronic properties clearly indicates that LaPtSi displays metallic behavior in both the spin-up and spin-down states. In the spin-up state of LaPdSi, a band gap is observed, which indicates its characteristic of being a half-metal. A comprehensive investigation of optical properties revealed that these compounds display notable absorption and optical conductivity at higher energy levels. Conversely, they exhibit transparency to incident photons at lower energy levels. Based on the findings, it can be concluded that these compounds are highly suitable for application in high-frequency UV devices. The thermoelectric properties clearly indicate that both materials exhibit high power factors, electrical conductivity, and figures of merit (ZT), suggesting their potential as exceptional thermoelectric materials. The simulations conducted in this study consider the effect of on-site Coulomb interactions by incorporating the Hubbard U term within the GGA + U. Our findings contribute valuable insights that can facilitate further experimental investigations and provide comprehensive validation.
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Affiliation(s)
- Mudasser Husain
- Department of Physics, University of Lakki Marwat 28420 Lakki Marwat KPK Pakistan
| | - Hind Albalawi
- Department of Physics, College of Sciences, Princess Nourah Bint Abdulrahman University (PNU) PO Box 84428 Riyadh 11671 Saudi Arabia
| | - Maryam Al Huwayz
- Department of Physics, College of Sciences, Princess Nourah Bint Abdulrahman University (PNU) PO Box 84428 Riyadh 11671 Saudi Arabia
| | - Rajwali Khan
- Department of Physics, University of Lakki Marwat 28420 Lakki Marwat KPK Pakistan
| | - Nasir Rahman
- Department of Physics, University of Lakki Marwat 28420 Lakki Marwat KPK Pakistan
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2
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Zhang G, Cui S, Zhang H, Feng Z, Wang G, Wang Q, Li Y, Liu C. High-pressure magnetic properties and electrical transport behaviors of half-metallic ferromagnet CrO 2. Phys Chem Chem Phys 2023; 25:7366-7372. [PMID: 36825775 DOI: 10.1039/d2cp05684d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
The magnetic properties and electrical transport behaviors of half-metallic ferromagnet chromium dioxide (CrO2) powders under high pressure have been investigated by in situ electrical resistivity, magneto-resistivity, and Hall-effect measurements. Our results reveal that the Hall coefficient, carrier concentration, and mobility all present discontinuous changes from 11.7 GPa to 14.9 GPa which can be attributed to the second-order structural transition from the rutile-type to CaCl2-type. However, the resistivity decreases monotonically from ambient pressure to 16.5 GPa. This is due to, first, the decreased carrier concentration and the increased carrier mobility canceling the effects of each other on the resistivity; second, according to the calculation results, the bandgap of CrO2 decreased gradually with the pressure, and the bandgaps of the rutile-type phase and the CaCl2-type phase are extremely similar. CrO2 exhibits a linear and negative magnetoresistance under the applied magnetic field (0∼ ± 15 kOe). As the pressure increases, the magnetoresistance remains negative, but it becomes nonlinear and less symmetric, suggesting that pressure has an appreciable impact on the double-exchange mechanism leading to ferromagnetism in CrO2.
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Affiliation(s)
- Guozhao Zhang
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science & Information Technology of Liaocheng University, Liaocheng 252059, China.
| | - Shouxin Cui
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science & Information Technology of Liaocheng University, Liaocheng 252059, China.
| | - Haiwa Zhang
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science & Information Technology of Liaocheng University, Liaocheng 252059, China.
| | - Zhenbao Feng
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science & Information Technology of Liaocheng University, Liaocheng 252059, China.
| | - Guangyu Wang
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science & Information Technology of Liaocheng University, Liaocheng 252059, China.
| | - Qinglin Wang
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science & Information Technology of Liaocheng University, Liaocheng 252059, China.
| | - Yinwei Li
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science & Information Technology of Liaocheng University, Liaocheng 252059, China. .,Laboratory of Quantum Functional Materials Design and Application, School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, China
| | - Cailong Liu
- Shandong Key Laboratory of Optical Communication Science and Technology, School of Physical Science & Information Technology of Liaocheng University, Liaocheng 252059, China.
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3
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Zhang Z, Cheng M, Fan Z, Liu Y, Wang D, Wang K, Xiong R, Lu Z. The high magnetoresistance performance of epitaxial half-metallic CrO 2-based magnetic junctions. Phys Chem Chem Phys 2023; 25:1848-1857. [PMID: 36602084 DOI: 10.1039/d2cp05015c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Half-metallic chromium dioxide (CrO2) is an ideal spintronic material due to its near-full spin polarization and ultralow Gilbert damping at room temperature. Based on theoretical calculations, we found that the tunneling magnetoresistance (TMR) ratios of the CrO2/XO2/CrO2 (X= Ti and Sn) magnetic tunnel junctions (MTJs) can reach up to the order of magnitude of 105%, and the magnetoresistance (MR) ratio of CrO2/RuO2/CrO2 magnetic junctions (MJs) can reach the order of magnitude of 104%. In addition, we succeeded in fabricating epitaxial CrO2-based MTJs (CrO2/TiO2/CrO2 and CrO2/TiO2/Co2FeAl) with TiO2 tunnel barriers of varying thickness. Evident TMR effects were observed for all CrO2-based MTJs with the highest MR ratio of 8.55% for the CrO2/TiO2/Co2FeAl MTJ at 10 K. The MR ratios of CrO2-based MTJs in our studies were lower than theoretical expectations, which could be due to the possible mixture of interface atoms and Cr magnetization reversal. Moreover, the existence of oxygen vacancies in the TiO2 tunnel barrier also weakened the TMR effect significantly due to increased spin scattering, and the annealing treatment in an oxygen atmosphere led to an increase in the MR ratio of the CrO2/TiO2/Co2FeAl MTJ by about 33% in comparison with the unannealed MTJ, which is consistent with theoretical calculations.
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Affiliation(s)
- Zhenhua Zhang
- The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China. .,School of Materials and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China
| | - Ming Cheng
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, China.
| | - Zhiqiang Fan
- School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114, China
| | - Yong Liu
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, China.
| | - Dengjing Wang
- College of Science, Wuhan University of Science and Technology, Wuhan 430065, China
| | - Ke Wang
- School of Mechanical and Electronic Engineering, East China University of Technology, Nanchang 330013, China
| | - Rui Xiong
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, China.
| | - Zhihong Lu
- The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China. .,School of Materials and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China
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4
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Qian L, Zhou S, Wang K, Xiao G. Resistance of single domain walls in half-metallic CrO 2 epitaxial nanostructures. NANOSCALE 2021; 13:20034-20040. [PMID: 34842890 DOI: 10.1039/d1nr05555k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Magnetic domain structures are active electron transport agents and can be used to induce large magnetoresistance (MR), particularly in half-metallic solids. We have studied the excess resistance induced by a single magnetic domain wall in a one-dimensional half-metallic CrO2 nanoscale conductor with a built-in constriction whose channel width (d) ranges from 30 to 200 nm. We observed that the domain wall-induced MR is enhanced by 70 fold when d decreases from 200 nm to 30 nm. We speculate that the enhancement is due to the increased domain wall resistance (DWR) and the extra contribution of ballistic magnetoresistance (BMR). We have uncovered a large size effect of d on the MR induced by the domain wall, which scales with d as d-1.87±0.32. Accordingly, we predict that the MR ratio of a simple CrO2 nanowire impregnated with a constriction at a 150 nm2 cross-section could reach 100%. This large MR far exceeds that of a conventional ferromagnetic nanowire, confirming the role of half metallicity on enhanced magneto-transport.
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Affiliation(s)
- Lijuan Qian
- Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
| | - Shiyu Zhou
- Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
| | - Kang Wang
- Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
| | - Gang Xiao
- Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
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5
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Shi JL, Wang Y, Zhao XJ, Zhang YZ, Yuan S, Wei SH, Zhang DB. Strain induced spin-splitting and half-metallicity in antiferromagnetic bilayer silicene under bending. Phys Chem Chem Phys 2020; 22:11567-11571. [PMID: 32400823 DOI: 10.1039/d0cp01350a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Searching for half-metals in low dimensional materials is not only of scientific importance, but also has important implications for the realization of spintronic devices on a small scale. In this work, we show theoretically that simple bending can induce spin-splitting in bilayer silicene. For bilayer silicene with Bernal stacking, the monolayer has a long range ferromagnetic spin order and between the two monolayers, the spin orders are opposite, giving rise to an antiferromagnetic configuration for the ground state of the bilayer silicene. Under bending, the antiferromagnetic spin order is retained but the energetic degeneracy of opposite spin states is lifted. Due to the unusual deformation potentials of the conduction band minimum (CBM) and valence band maximum (VBM) as revealed by density-functional theory calculations and density-functional tight-binding calculations, this spin-splitting is nearly proportional to the degree of bending deformation. Consequently, the spin-splitting can be significant and the desired half-metallic state may emerge when the bending increases, which has been verified by direct simulation of the bent bilayer silicene using the generalized Bloch theorem. Our results hint that bilayer silicene may be an excellent candidate for half-metallicity.
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Affiliation(s)
- Jin-Lei Shi
- Beijing Computational Science Research Center, Beijing, 100193, P. R. China.
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6
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Shi JL, Zhao XJ, Seifert G, Wei SH, Zhang DB. Unconventional deformation potential and half-metallicity in zigzag nanoribbons of 2D-Xenes. Phys Chem Chem Phys 2020; 22:7294-7299. [PMID: 32211628 DOI: 10.1039/c9cp06416h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Realization of half-metallicity (HM) in low dimensional materials is a fundamental challenge for nano spintronics and a critical component for developing alternative generations of information technology. Using first-principles calculations, we reveal an unconventional deformation potential for zigzag nanoribbons (NRs) of 2D-Xenes. Both the conduction band minimum (CBM) and valence band maximum (VBM) of the edge states have negative deformation potentials. This unique property, combined with the localization and spin-polarization of the edge states, enables us to induce spin-splitting and HM using an inhomogeneous strain pattern, such as simple in-plane bending. Indeed, our calculation using the generalized Bloch theorem reveals the predicted HM in bent zigzag silicene NRs. Furthermore, the magnetic stability of the long range magnetic order for the spin-polarized edge states is maintained well against the bending deformation. These aspects indicate that it is a promising approach to realize HM in low dimensions with the zigzag 2D-Xene NRs.
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Affiliation(s)
- Jin-Lei Shi
- Beijing Computational Science Research Center, Beijing 100193, P. R. China.
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7
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Qian L, Chen W, Xiao G. Spin curvature induced resistivity in epitaxial half-metallic CrO 2 thin films. NANOSCALE 2020; 12:3958-3964. [PMID: 32010911 DOI: 10.1039/c9nr09443a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Spin configuration inside a ferromagnetic metal influences its magnetoresistive behavior. The local spin curvature induces excess resistivity from the homogeneous ferromagnetic state. In this work, we characterize the spin curvature induced resistivity in epitaxial half-metallic CrO2 nanowires with 100% spin polarization. We control the magnitude of the spin curvature by introducing different geometric notches along the edge of the wire and applying an external magnetic field. Through magnetoresistance measurements and micromagnetic simulations, we uncover an empirical relationship between the spin curvature and the induced resistivity in this archetypal half-metallic solid. This relationship provides a quantitative method to calculate the resistance of magnetic domain walls or other spin textured states. We also study the influence of the thermal effect on the spin curvature induced resistivity across temperatures ranging from 10 K to 250 K. Thermal magnons worsen spin asymmetry considerably and suppress spin curvature induced resistivity at temperatures much lower than the ferromagnetic ordering temperature Tc.
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Affiliation(s)
- Lijuan Qian
- Department of Physics, Brown University, Providence, RI 02912, USA.
| | - Wenzhe Chen
- Department of Physics, Brown University, Providence, RI 02912, USA.
| | - Gang Xiao
- Department of Physics, Brown University, Providence, RI 02912, USA.
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8
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Kamboj S, Roy DK, Roy S, Chowdhury RR, Mandal P, Kabir M, Sheet G. Temperature dependent transport spin-polarization in the low Curie temperature complex itinerant ferromagnet EuTi 1-x Nb x O 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:415601. [PMID: 31239429 DOI: 10.1088/1361-648x/ab2cbd] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The physical systems with ferromagnetism and 'bad' metallicity hosting unusual transport properties are playgrounds of novel quantum phenomena. Recently EuTi1-x Nb x O3 emerged as a ferromagnetic system where non-trivial temperature dependent transport properties are observed due to coexistence and competition of various magnetic and non-magnetic scattering processes. In the ferromagnetic state, the resistivity shows a T 2 temperature dependence possibly due to electron-magnon scattering and above the Curie temperature [Formula: see text], the dependence changes to T 3/2 behaviour indicating a correlation between transport and magnetic properties. In this paper, we show that the transport spin-polarization ([Formula: see text]) in EuTi1-x Nb x O3, a low Curie temperature ferromagnet, is as high (∼40%) as that in some of the metallic ferromagnets with high Curie temperatures. In addition, owing to the low Curie temperature of EuTi1-x Nb x O3, the temperature (T) dependence of [Formula: see text] could be measured systematically up to [Formula: see text] which revealed a proportionate relationship with magnetization [Formula: see text] versus T. This indicates that such proportionality is far more universally valid than the ferromagnets with ideal parabolic bands. Furthermore, our band structure calculations not only helped to understand the origin of such high spin polarization in EuTi1-x Nb x O3 but also provided a route to estimate the Hubbard U parameter in complex metallic ferromagnets in general using experimental inputs.
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Affiliation(s)
- Suman Kamboj
- Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, S. A. S. Nagar, Manauli, PO: 140306, India
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9
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Han J, Shen J, Gao G. CrO 2-based heterostructure and magnetic tunnel junction: perfect spin filtering effect, spin diode effect and high tunnel magnetoresistance. RSC Adv 2019; 9:3550-3557. [PMID: 35518069 PMCID: PMC9060253 DOI: 10.1039/c8ra08107g] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Accepted: 01/17/2019] [Indexed: 11/25/2022] Open
Abstract
Half-metallic ferromagnetic CrO2 has attracted much interest due to its 100% spin polarization and high Curie temperature. CrO2 films have been fabricated on a TiO2 (100) substrate. However, there have been no reports on the spin transport properties of devices based on a CrO2 electrode and TiO2 barrier. In this work, we use first-principles calculations combined with a nonequilibrium Green's function method to investigate the bias-voltage-dependent spin transport properties for the CrO2/TiO2 (100) heterostructure and the CrO2/TiO2/CrO2 (100) magnetic tunnel junction (MTJ). Our results reveal the excellent spin filtering effect and spin diode effect in the heterostructure as well as the high tunnel magnetoresistance ratio (up to 4.48 × 1014%) in the MTJ, which indicate potential spintronic applications. The origins of these perfect spin transport characteristics are discussed in terms of the calculated spin-dependent electrode band structures, the spin-dependent transmission spectra and semiconductor theory. Spin-dependent device density of states in the CrO2/TiO2/CrO2 magnetic tunnel junction.![]()
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Affiliation(s)
- Jiangchao Han
- School of Physics, Huazhong University of Science and Technology Wuhan 430074 China
| | - Jimei Shen
- Nanjing Normal University Taizhou College Taizhou 225300 China
| | - Guoying Gao
- School of Physics, Huazhong University of Science and Technology Wuhan 430074 China .,Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology Wuhan 430074 China
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Yates KA, Cohen LF. Andreev reflection spectroscopy in transition metal oxides. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:20150001. [PMID: 29941621 PMCID: PMC6030146 DOI: 10.1098/rsta.2015.0001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/07/2018] [Indexed: 06/08/2023]
Abstract
Here we review the literature concerning measurement of the Andreev reflection between a superconductor (S) and ferromagnet (F), with particular attention to the case where the ferromagnet is a transition metal oxide. We discuss the practicality of utilization of the current models for determination of the transport current spin polarization and examine the evidence for Andreev bound states.This article is part of the theme issue 'Andreev bound states'.
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Affiliation(s)
- Karen A Yates
- Physics Department, The Blackett Laboratory, Imperial College London, London SW7 2AZ, UK
| | - Lesley F Cohen
- Physics Department, The Blackett Laboratory, Imperial College London, London SW7 2AZ, UK
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11
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Cheng M, Lu Z, Zhang Z, Yu Z, Liu S, Chen C, Li Y, Liu Y, Shi J, Xiong R. Manipulation of film quality and magnetic properties of CrO2 (100) films on TiO2 substrates with carrier gas and growth temperature. RSC Adv 2018; 8:1562-1568. [PMID: 35540879 PMCID: PMC9077135 DOI: 10.1039/c7ra10874e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Accepted: 12/20/2017] [Indexed: 11/21/2022] Open
Abstract
High-quality CrO2 films were synthesized on TiO2 (100) substrates at different temperatures using the chemical vapor deposition method in argon or nitrogen atmosphere. It was found that the lower limit for the growth temperature of CrO2 films can be reduced to 310 or 300 °C when using Ar or N2 as the carrier gas, respectively. The quality of CrO2 film on TiO2 substrate can thus be improved by optimizing growth temperature in a much larger range (310–400 °C in Ar and 300–430 °C in N2, in contrast with 390–410 °C in O2), which is significant for the practical application of CrO2 films. The best film quality was achieved at 320 °C in either Ar or N2 atmosphere, at which CrO2 film has its narrowest orientation distribution and lowest roughness. Compared to films grown in O2, films grown in Ar were found to have larger saturation magnetizations (Ms) and magnetic anisotropies, possibly due to numerous O vacancies. Films grown in N2 are actually N-doped films, and have lower Ms than those grown in O2. The Curie temperature (Tc) was also tuned by the carrier gas and growth temperature. Films grown in Ar or N2 generally have a higher Tc value than those grown in O2. Furthermore, the thermal stability of the films was found to be remarkably improved when using N2 as the carrier gas. The quality and properties of CrO2 films can be manipulated by changing the carrier gas and varying the deposition temperature.![]()
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12
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Rozhkov AV, Rakhmanov AL, Sboychakov AO, Kugel KI, Nori F. Spin-Valley Half-Metal as a Prospective Material for Spin Valleytronics. PHYSICAL REVIEW LETTERS 2017; 119:107601. [PMID: 28949193 DOI: 10.1103/physrevlett.119.107601] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Indexed: 06/07/2023]
Abstract
Half-metallicity (full spin polarization of the Fermi surface) usually occurs in strongly correlated electron systems. We demonstrate that doping a spin-density wave insulator in the weak-coupling regime may also stabilize half-metallic states. In the absence of doping, the spin-density wave is formed by four nested bands [i.e., each band is characterized by charge (electron or hole) and spin (up or down) labels]. Of these four bands, only two accumulate the charge carriers introduced by doping, forming a half-metallic two-valley Fermi surface. Depending on the parameters, the spin polarizations of the electronlike and holelike valleys may be either (i) parallel or (ii) antiparallel. The Fermi surface of (i) is fully spin polarized (similar to usual half-metals). Case (ii), referred to as "a spin-valley half-metal," corresponds to complete polarization with respect to the spin-valley operator. The properties of these states are discussed.
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Affiliation(s)
- A V Rozhkov
- Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198 Japan
- Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow 125412 Russia
- Moscow Institute for Physics and Technology (State University), Dolgoprudnyi 141700 Russia
| | - A L Rakhmanov
- Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198 Japan
- Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow 125412 Russia
- Moscow Institute for Physics and Technology (State University), Dolgoprudnyi 141700 Russia
- Dukhov Research Institute of Automatics, Moscow 127055 Russia
| | - A O Sboychakov
- Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198 Japan
- Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow 125412 Russia
| | - K I Kugel
- Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow 125412 Russia
- National Research University Higher School of Economics, Moscow 101000 Russia
| | - Franco Nori
- Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198 Japan
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040, USA
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13
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Hellman F, Hoffmann A, Tserkovnyak Y, Beach GSD, Fullerton EE, Leighton C, MacDonald AH, Ralph DC, Arena DA, Dürr HA, Fischer P, Grollier J, Heremans JP, Jungwirth T, Kimel AV, Koopmans B, Krivorotov IN, May SJ, Petford-Long AK, Rondinelli JM, Samarth N, Schuller IK, Slavin AN, Stiles MD, Tchernyshyov O, Thiaville A, Zink BL. Interface-Induced Phenomena in Magnetism. REVIEWS OF MODERN PHYSICS 2017; 89:025006. [PMID: 28890576 PMCID: PMC5587142 DOI: 10.1103/revmodphys.89.025006] [Citation(s) in RCA: 181] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.
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Affiliation(s)
- Frances Hellman
- Department of Physics, University of California, Berkeley, Berkeley, California 94720, USA; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Axel Hoffmann
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - Yaroslav Tserkovnyak
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Geoffrey S D Beach
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Eric E Fullerton
- Center for Memory and Recording Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0401, USA
| | - Chris Leighton
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Allan H MacDonald
- Department of Physics, University of Texas at Austin, Austin, Texas 78712-0264, USA
| | - Daniel C Ralph
- Physics Department, Cornell University, Ithaca, New York 14853, USA; Kavli Institute at Cornell, Cornell University, Ithaca, New York 14853, USA
| | - Dario A Arena
- Department of Physics, University of South Florida, Tampa, Florida 33620-7100, USA
| | - Hermann A Dürr
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Peter Fischer
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA; Physics Department, University of California, 1156 High Street, Santa Cruz, California 94056, USA
| | - Julie Grollier
- Unité Mixte de Physique CNRS/Thales and Université Paris Sud 11, 1 Avenue Fresnel, 91767 Palaiseau, France
| | - Joseph P Heremans
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, Ohio 43210, USA; Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, USA; Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Tomas Jungwirth
- Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, 162 53 Praha 6, Czech Republic; School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Alexey V Kimel
- Radboud University, Institute for Molecules and Materials, Nijmegen 6525 AJ, The Netherlands
| | - Bert Koopmans
- Department of Applied Physics, Center for NanoMaterials, COBRA Research Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - Ilya N Krivorotov
- Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
| | - Steven J May
- Department of Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania 19104, USA
| | - Amanda K Petford-Long
- Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, USA; Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, Illinois 60208, USA
| | - James M Rondinelli
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - Nitin Samarth
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ivan K Schuller
- Department of Physics and Center for Advanced Nanoscience, University of California, San Diego, La Jolla, California 92093, USA; Materials Science and Engineering Program, University of California, San Diego, La Jolla, California 92093, USA
| | - Andrei N Slavin
- Department of Physics, Oakland University, Rochester, Michigan 48309, USA
| | - Mark D Stiles
- Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6202, USA
| | - Oleg Tchernyshyov
- Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - André Thiaville
- Laboratoire de Physique des Solides, UMR CNRS 8502, Université Paris-Sud, 91405 Orsay, France
| | - Barry L Zink
- Department of Physics and Astronomy, University of Denver, Denver, CO 80208, USA
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14
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Xu TS, Ju L, Wang Z, Ren C, Kang SS, Qiao SZ, Li TX, Yan SS, Mei LM. Disorder-enhanced spin polarization of the Zn 1−xCo xO 1−v concentrated magnetic semiconductor. RSC Adv 2016. [DOI: 10.1039/c5ra20520d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Amorphous concentrated magnetic semiconductor Zn0.32Co0.68O1−v (v refers to oxygen vacancies) thin film was investigated by magnetic and electrical transport measurements as well as Andreev reflection spectroscopy.
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Affiliation(s)
- T. S. Xu
- School of Physics and Electrical Engineering
- Anyang Normal College
- Anyang 455000
- People's Republic of China
- School of Physics
| | - L. Ju
- School of Physics and Electrical Engineering
- Anyang Normal College
- Anyang 455000
- People's Republic of China
| | - Z. Wang
- School of Physics and Electrical Engineering
- Anyang Normal College
- Anyang 455000
- People's Republic of China
| | - C. Ren
- National Laboratory for Superconductivity
- Institute of Physics
- Chinese Academy of Sciences
- Beijing 100190
- People's Republic of China
| | - S. S. Kang
- School of Physics
- National Key Laboratory of Crystal Materials
- Shandong University
- Jinan 250100
- People's Republic of China
| | - S. Z. Qiao
- School of Physics
- National Key Laboratory of Crystal Materials
- Shandong University
- Jinan 250100
- People's Republic of China
| | - T. X. Li
- School of Physics and Electrical Engineering
- Anyang Normal College
- Anyang 455000
- People's Republic of China
| | - S. S. Yan
- School of Physics
- National Key Laboratory of Crystal Materials
- Shandong University
- Jinan 250100
- People's Republic of China
| | - L. M. Mei
- School of Physics
- National Key Laboratory of Crystal Materials
- Shandong University
- Jinan 250100
- People's Republic of China
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15
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Guan T, Lin C, Yang C, Shi Y, Ren C, Li Y, Weng H, Dai X, Fang Z, Yan S, Xiong P. Evidence for Half-Metallicity in n-type HgCr2Se4. PHYSICAL REVIEW LETTERS 2015; 115:087002. [PMID: 26340201 DOI: 10.1103/physrevlett.115.087002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Indexed: 06/05/2023]
Abstract
High quality HgCr2Se4 single crystals have been investigated by magnetization, electron transport, and Andreev reflection spectroscopy. In the ferromagnetic ground state, the saturation magnetic moment of each unit cell corresponds to an integer number of electron spins (3 μB/Cr3+), and the Hall effect measurements suggest n-type charge carriers. Spin polarizations as high as 97% were obtained from fits of the differential conductance spectra of HgCr2Se4/Pb junctions with the modified Blonder-Tinkham-Klapwijk theory. The temperature and bias-voltage dependencies of the subgap conductance are consistent with recent theoretical calculations based on spin active scatterings at a superconductor-half-metal interface. Our results suggest that n-HgCr2Se4 is a half-metal, in agreement with theoretical calculations that also predict undoped HgCr2Se4 is a magnetic Weyl semimetal.
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Affiliation(s)
- Tong Guan
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Chaojing Lin
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Chongli Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Youguo Shi
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Cong Ren
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Yongqing Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Hongming Weng
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Xi Dai
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Zhong Fang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China and Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Shishen Yan
- School of Physics, Shandong University, Jinan 250100, China
| | - Peng Xiong
- Department of Physics, Florida State University, Tallahassee, Florida 32306, USA
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16
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Hwang I, Lee K, Jin H, Choi S, Jung E, Park BH, Lee S. A new simple method for point contact Andreev reflection (PCAR) using a self-aligned atomic filament in transition-metal oxides. NANOSCALE 2015; 7:8531-8535. [PMID: 25895727 DOI: 10.1039/c4nr07262f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Point contact Andreev reflection (PCAR) has become a standard method for measuring the spin polarization (P) of spintronic materials due to its unique simplicity and the firm physical ground, but it is still challenging to achieve a clean point contact between a superconductor (SC) and a metal (N) for implementing PCAR. In this work, we suggest a much simpler method for PCAR measurement, where a point contact between SC and N is provided by a metallic filament in a transition-metal oxide generated by electrical bias. This method has been successfully demonstrated using a structure composed of Nb/NiO/Pt, where P of the Ni filament was estimated to be about 40%, consistent with the known value of the bulk Ni. In addition, we investigated the dependence of the conductance spectrum on the measurement temperature and the magnetic field. We found that the superconductivity is not fully suppressed until 9 T far above the critical field of Nb, which is associated with the nm-sized constriction of our SC/N junction, much smaller than the coherence length of the SC.
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Affiliation(s)
- Inrok Hwang
- Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
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17
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Abstract
Collective spin excitations form a fundamental class of excitations in magnetic materials. As their energy reaches down to only a few meV, they are present at all temperatures and substantially influence the properties of magnetic systems. To study the spin excitations in solids from first principles, we have developed a computational scheme based on many-body perturbation theory within the full-potential linearized augmented plane-wave (FLAPW) method. The main quantity of interest is the dynamical transverse spin susceptibility or magnetic response function, from which magnetic excitations, including single-particle spin-flip Stoner excitations and collective spin-wave modes as well as their lifetimes, can be obtained. In order to describe spin waves we include appropriate vertex corrections in the form of a multiple-scattering T matrix, which describes the coupling of electrons and holes with different spins. The electron-hole interaction incorporates the screening of the many-body system within the random-phase approximation. To reduce the numerical cost in evaluating the four-point T matrix, we exploit a transformation to maximally localized Wannier functions that takes advantage of the short spatial range of electronic correlation in the partially filled d or f orbitals of magnetic materials. The theory and the implementation are discussed in detail. In particular, we show how the magnetic response function can be evaluated for arbitrary k points. This enables the calculation of smooth dispersion curves, allowing one to study fine details in the k dependence of the spin-wave spectra. We also demonstrate how spatial and time-reversal symmetry can be exploited to accelerate substantially the computation of the four-point quantities. As an illustration, we present spin-wave spectra and dispersions for the elementary ferromagnet bcc Fe, B2-type tetragonal FeCo, and CrO₂ calculated with our scheme. The results are in good agreement with available experimental data.
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18
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Chen TY, Chien CL. Chen and Chien reply. PHYSICAL REVIEW LETTERS 2013; 111:139704. [PMID: 24116825 DOI: 10.1103/physrevlett.111.139704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Indexed: 06/02/2023]
Affiliation(s)
- T Y Chen
- Department of Physics, Arizona State University, Tempe, Arizona 85287, USA
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19
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Yuan JJ, Wen GH, Zhao Q, Fan YB, Zhang CP, Zhang XK, Yu HJ, Xie YM. Preparation and magnetic properties of submicron CrO2 thin film on poly-crystal TiO2 film. Chem Res Chin Univ 2013. [DOI: 10.1007/s40242-013-2382-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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20
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Chen TY, Tesanovic Z, Chien CL. Unified formalism of Andreev reflection at a ferromagnet/superconductor interface. PHYSICAL REVIEW LETTERS 2012; 109:146602. [PMID: 23083265 DOI: 10.1103/physrevlett.109.146602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Indexed: 06/01/2023]
Abstract
We present a unified formalism of Andreev reflection of a partial polarized current at a ferromagnet/superconductor interface instead of assuming a linear combination of unpolarized and polarized currents. The Andreev reflection is limited by the states of minority spins and the extra majority spins become evanescent wave. We further study the effects of spin polarization, inelastic scattering, and interfacial scattering on the Andreev reflection, normal reflection, and transmitted probabilities in equilibrium as well as under a bias. Our model, which reduces to those of Blonder, Tinkham, and Klapwijk, Mazin, and Dynes in three limiting cases, provides a significantly better description of the experimental results.
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Affiliation(s)
- T Y Chen
- Department of Physics, Arizona State University, Tempe, Arizona 85287, USA
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21
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Nurbawono A, Zhang C. Sensing with superconducting point contacts. SENSORS 2012; 12:6049-74. [PMID: 22778630 PMCID: PMC3386729 DOI: 10.3390/s120506049] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Revised: 04/06/2012] [Accepted: 04/20/2012] [Indexed: 11/17/2022]
Abstract
Superconducting point contacts have been used for measuring magnetic polarizations, identifying magnetic impurities, electronic structures, and even the vibrational modes of small molecules. Due to intrinsically small energy scale in the subgap structures of the supercurrent determined by the size of the superconducting energy gap, superconductors provide ultrahigh sensitivities for high resolution spectroscopies. The so-called Andreev reflection process between normal metal and superconductor carries complex and rich information which can be utilized as powerful sensor when fully exploited. In this review, we would discuss recent experimental and theoretical developments in the supercurrent transport through superconducting point contacts and their relevance to sensing applications, and we would highlight their current issues and potentials. A true utilization of the method based on Andreev reflection analysis opens up possibilities for a new class of ultrasensitive sensors.
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Affiliation(s)
- Argo Nurbawono
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore; E-Mail: argo
| | - Chun Zhang
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore; E-Mail: argo
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore
- Author to whom correspondence should be addressed; E-Mail:
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22
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Verma V, Ahmad S, Dar A, Kotnala R. An Inexpensive Route to Synthesize High-Purity CrO2 for EMI Shielding in X-Band Frequencies. ACTA ACUST UNITED AC 2012. [DOI: 10.5402/2012/948219] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Rod-shaped high-purity samples of CrO2 have been synthesized by an inexpensive and simplified procedure. Here, we have prepared pure CrO2 without applying any external pressure or control it during synthesis. The sample prepared exhibited an improvement in saturation magnetization values, 68 emu/g at 300 K, 136 emu/g at 80 K, and uniform grained microstructure. The complex permittivity, permeability, and microwave absorption properties of high-purity CrO2 sample were investigated in the 8.2–12.2 GHz (X-band) microwave frequency range. Microwave measurements have shown the high shielding effectiveness due to absorption (SEA) of 20.3 dB. The high value of SEA suggests that CrO2 can be used as a promising electromagnetic shielding, EMI, material in 8.2–12.2 GHz (X-band) microwave frequency range.
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Affiliation(s)
- Vivek Verma
- Magnetic Standards, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110 012, India
- Department of Physics, Hindu College, University of Delhi, Delhi 110007, India
| | - Shahab Ahmad
- Magnetic Standards, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110 012, India
| | - Abdullah Dar
- Magnetic Standards, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110 012, India
| | - R. Kotnala
- Magnetic Standards, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110 012, India
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23
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Tian Y, Bakaul SR, Wu T. Oxide nanowires for spintronics: materials and devices. NANOSCALE 2012; 4:1529-1540. [PMID: 22293913 DOI: 10.1039/c2nr11767c] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Spintronics, or spin-based data storage and manipulation technology, is emerging as a very active research area because of both new science and potential technological applications. As the characteristic lengths of spin-related phenomena naturally fall into the nanometre regime, researchers start applying the techniques of bottom-up nanomaterial synthesis and assembly to spintronics. It is envisaged that novel physics regarding spin manipulation and domain dynamics can be realized in quantum confined nanowire-based devices. Here we review the recent breakthroughs related to the applications of oxide nanowires in spintronics from the perspectives of both material candidates and device fabrication. Oxide nanowires generally show excellent crystalline quality and tunable physical properties, but more efforts are imperative as we strive to develop novel spintronic nanowires and devices.
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Affiliation(s)
- Yufeng Tian
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637371, Singapore
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24
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Degrave JP, Schmitt AL, Selinsky RS, Higgins JM, Keavney DJ, Jin S. Spin polarization measurement of homogeneously doped Fe(1-x)Co(x)Si nanowires by Andreev reflection spectroscopy. NANO LETTERS 2011; 11:4431-4437. [PMID: 21923114 DOI: 10.1021/nl2026426] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We report a general method for determining the spin polarization from nanowire materials using Andreev reflection spectroscopy implemented with a Nb superconducting contact and common electron-beam lithography device fabrication techniques. This method was applied to magnetic semiconducting Fe(1-x)Co(x)Si alloy nanowires with x̅ = 0.23, and the average spin polarization extracted from 6 nanowire devices is 28 ± 7% with a highest observed value of 35%. Local-electrode atom probe tomography (APT) confirms the homogeneous distribution of Co atoms in the FeSi host lattice, and X-ray magnetic circular dichroism (XMCD) establishes that the elemental origin of magnetism in this strongly correlated electron system is due to Co atoms.
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Affiliation(s)
- John P Degrave
- Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States
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25
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Dowben PA, Wu N, Binek C. When measured spin polarization is not spin polarization. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:171001. [PMID: 21474881 DOI: 10.1088/0953-8984/23/17/171001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO(2) and Cr(2)O(3) illustrate some of the complications which hinders comparisons of spin polarization values.
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Affiliation(s)
- P A Dowben
- Department of Physics and Astronomy, University of Nebraska, 855 Jorgensen Hall, North 16th Street, PO Box 880299, Lincoln, NE 68588-0111, USA.
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26
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Zhao Q, Wen G, Liu Z, Fan Y, Zou G, Li L, Zheng R, Ringer SP, Mao HK. Synthesis of dense, single-crystalline CrO2 nanowire arrays using AAO template-assisted chemical vapor deposition. NANOTECHNOLOGY 2011; 22:125603. [PMID: 21325713 DOI: 10.1088/0957-4484/22/12/125603] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
High-density, vertically aligned CrO(2) nanowire arrays were obtained via atmospheric-pressure CVD assisted by AAO templates. The CrO(2) nanowire arrays show remarkably enhanced coercivity compared with CrO(2) films or bulk. It was found that the length of the nanowires is greatly influenced by the pore diameter of the AAO template used. The growth mechanism and the pore size dependence of the CrO(2) nanowire arrays are discussed. The present method provides a useful approach for the synthesis of CrO(2) nanowire arrays. Such highly ordered nanowire arrays within an AAO template may have important applications in ultrahigh-density perpendicular magnetic recording devices and the mass production of spintronic nanodevices.
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Affiliation(s)
- Qiang Zhao
- State Key Laboratory of Superhard Materials, Jilin University, Changchun, People's Republic of China
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27
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Gao GY, Yao KL, Li N. Preserving the half-metallicity at the surfaces of rocksalt CaN and SrN and the interfaces of CaN/InN and SrN/GaP: a density functional study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:075501. [PMID: 21411884 DOI: 10.1088/0953-8984/23/7/075501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Recent theoretical studies indicate that metastable rocksalt CaN, SrN, and BaN exhibit half-metallic ferromagnetism (Volnianska and Boguslawski 2007 Phys. Rev. B 75 224418; Gao et al 2008 Phys. Lett. A 372 1512), and further experiments confirm the existence of self-assembled metastable CaN nanostructures (Liu et al 2008 Surf. Sci. 602 1844). We here use the first-principles method based on density functional theory to investigate the structural, electronic, and magnetic properties of the (111) surfaces of CaN and SrN and the interfaces of CaN/InN(111) and SrN/GaP(111). The surface stability from the calculated surface energy indicates that the N-terminated (111) surface is more stable than the Ca (Sr)-terminated (111) surface in the N-rich environment. For CaN and SrN, both anion- and cation-terminated (111) surfaces preserve the half-metallic characteristics of the bulk. Interfacial studies indicate that the half-metallicity of bulk CaN is retained in two of the four possible configurations of the CaN/InN(111) interface, while for the interface of SrN/GaP(111) only one interfacial configuration shows half-metallicity. Furthermore, we assess the interfacial adhesive strength for all the possible different configurations of the interfaces studied here by calculating the interface adhesion energies.
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Affiliation(s)
- G Y Gao
- School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China. guoying
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28
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Löfwander T, Grein R, Eschrig M. Is CrO2 fully spin polarized? Analysis of Andreev spectra and excess current. PHYSICAL REVIEW LETTERS 2010; 105:207001. [PMID: 21231255 DOI: 10.1103/physrevlett.105.207001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Indexed: 05/30/2023]
Abstract
We report an extensive theoretical analysis of point-contact Andreev reflection data available in the literature on ferromagnetic CrO2. We find that the spectra can be well understood within a model of fully spin-polarized bands in CrO2 together with spin-active scattering at the contact. This is in contrast to analysis of the data within extended Blonder-Tinkham-Klapwijk models, which lead to a spin polarization varying between 50% and 100% depending on the transparency of the interface. We propose to utilize both the temperature dependence of the spectra and the excess current at voltages above the gap to resolve the spin polarization in CrO2 in a new generation of experiments.
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Affiliation(s)
- Tomas Löfwander
- Department of Microtechnology and Nanoscience-MC2, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
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29
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Utfeld C, Giblin SR, Taylor JW, Duffy JA, Shenton-Taylor C, Laverock J, Dugdale SB, Manno M, Leighton C, Itou M, Sakurai Y. Bulk spin polarization of Co(1-x)Fe(x)S2. PHYSICAL REVIEW LETTERS 2009; 103:226403. [PMID: 20366116 DOI: 10.1103/physrevlett.103.226403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Indexed: 05/29/2023]
Abstract
We report on a new method to determine the degree of bulk spin polarization in single crystal Co(1-x)Fe(x)S2 by modeling magnetic Compton scattering with ab initio calculations. Spin-dependent Compton profiles were measured for CoS2 and Co0.9Fe0.1S2. The ab initio calculations were then refined by rigidly shifting the bands to provide the best fit between the calculated and experimental directional profiles for each sample. The bulk spin polarizations, P, corresponding to the spin-polarized density of states at the Fermi level, were then extracted from the refined calculations. The values were found to be P=-72+/-6% and P=18+/-7% for CoS2 and Co0.9Fe0.1S2, respectively. Furthermore, determinations of P weighted by the Fermi velocity (v(F) or v(F)2) were obtained, permitting a rigorous comparison with other experimental data and highlighting the experimental dependence of P on v(F).
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Affiliation(s)
- C Utfeld
- H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
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30
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Zhao Q, Wen G, Liu Z, Yuan J, Li D, Zou G, Zheng R, Ringer SP, Mao HK. High-density, vertically aligned crystalline CrO2 nanorod arrays derived from chemical vapor deposition assisted by AAO templates. Chem Commun (Camb) 2009:3949-51. [DOI: 10.1039/b905308e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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31
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Stokmaier M, Goll G, Weissenberger D, Sürgers C, Löhneysen HV. Size dependence of current spin polarization through superconductor/ferromagnet nanocontacts. PHYSICAL REVIEW LETTERS 2008; 101:147005. [PMID: 18851563 DOI: 10.1103/physrevlett.101.147005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2007] [Indexed: 05/26/2023]
Abstract
The spin polarization P of the transport current through the interface between superconducting Al and ferromagnetic Fe is determined by means of Andreev reflection at nanostructured point contacts. We observe a systematic decrease of P with decreasing contact resistance. Our data provide evidence for the reduction of P by spin-orbit scattering and thus establish a link between density of states and transport spin polarizations.
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Affiliation(s)
- M Stokmaier
- Physikalisches Institut, Universität Karlsruhe, 76128 Karlsruhe, Germany
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32
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Song Y, Schmitt AL, Jin S. Spin-dependent tunneling transport into CrO2 nanorod devices with nonmagnetic contacts. NANO LETTERS 2008; 8:2356-2361. [PMID: 18616325 DOI: 10.1021/nl080038q] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Single-crystal nanorods of half-metallic chromium dioxide (CrO2) were synthesized and structurally characterized. Spin-dependent electrical transport was investigated in individual CrO2 nanorod devices contacted with nonmagnetic metallic electrodes. Negative magnetoresistance (MR) was observed at low temperatures due to the spin-dependent direct tunneling through the contact barrier and the high spin polarization in the half-metallic nanorods. The magnitude of this negative magnetoresistance decreases with increasing bias voltage and temperature due to spin-independent inelastic hopping through the barrier, and a small positive magnetoresistance was found at room temperature. It is believed that the contact barrier and the surface state of the nanorods have great influence on the spin-dependent transport limiting the magnitude of MR effect in this first attempt at spin filter devices of CrO2 nanorods with nonmagnetic contacts.
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Affiliation(s)
- Yipu Song
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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33
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Sousa P, Dias S, Conde O, Silvestre A, Branford W, Morris B, Yates K, Cohen L. Influence of Growth Temperature and Carrier Flux on the Structure and Transport Properties of Highly Oriented CrO2 on Al2O3 (0001). ACTA ACUST UNITED AC 2007. [DOI: 10.1002/cvde.200706592] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Leighton C, Manno M, Cady A, Freeland JW, Wang L, Umemoto K, Wentzcovitch RM, Chen TY, Chien CL, Kuhns PL, Hoch MJR, Reyes AP, Moulton WG, Dahlberg ED, Checkelsky J, Eckert J. Composition controlled spin polarization in Co(1-x)Fe(x)S(2) alloys. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2007; 19:315219. [PMID: 21694119 DOI: 10.1088/0953-8984/19/31/315219] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The transition metal (TM) chalcogenides of the form TMX(2) (X = S or Se) have been studied for decades due to their interesting electronic and magnetic properties such as metamagnetism and metal-insulator transitions. In particular, the Co(1-x)Fe(x)S(2) alloys were the subject of investigation in the 1970s due to general interest in itinerant ferromagnetism. In recent years (2000-present) it has been shown, both by electronic structure calculations and detailed experimental investigations, that Co(1-x)Fe(x)S(2) is a model system for the investigation of highly spin polarized ferromagnetism. The radically different electronic properties of the two endpoint compounds (CoS(2) is a narrow bandwidth ferromagnetic metal, while FeS(2) is a diamagnetic semiconductor), in a system forming a substitutional solid solution allows for composition control of the Fermi level relative to the spin split bands, and therefore composition-controlled conduction electron spin polarization. In essence, the recent work has shown that the concept of 'band engineering' can be applied to half-metallic ferromagnets and that high spin polarization can be deliberately engineered. Experiments reveal tunability in both sign and magnitude of the spin polarization at the Fermi level, with maximum values obtained to date of 85% at low temperatures. In this paper we review the properties of Co(1-x)Fe(x)S(2) alloys, with an emphasis on properties of relevance to half-metallicity. Crystal structure, electronic structure, synthesis, magnetic properties, transport properties, direct probes of the spin polarization, and measurements of the total density of states at the Fermi level are all discussed. We conclude with a discussion of the factors that influence, or even limit, the spin polarization, along with a discussion of opportunities and problems for future investigation, particularly with regard to fundamental studies of spintronic devices.
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Affiliation(s)
- C Leighton
- Department of Chemical Engineering and Materials Science, University of Minnesota, USA
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Tobin JG, Morton SA, Yu SW, Waddill GD, Schuller IK, Chambers SA. Spin resolved photoelectron spectroscopy of Fe(3)O(4): the case against half-metallicity. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2007; 19:315218. [PMID: 21694118 DOI: 10.1088/0953-8984/19/31/315218] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Many materials have been theoretically predicted to be half-metallic, and hence suitable for use as pure spin sources in spintronic devices. Yet to date, remarkably few of these predictions have been experimentally verified. We have used spin polarized photoelectron spectroscopy to study one candidate half-metallic system, Fe(3)O(4). Such experiments are normally hampered by difficulties in producing clean stoichiometric surfaces with a polarization that is truly representative of that of the bulk. However, by utilizing higher photon energies than have traditionally been used for such experiments, we can study polarization in 'as received' samples, essentially 'looking through' the disrupted surface. High quality, strain relieved, ex situ prepared Fe(3)O(4) films have been thoroughly characterized by diffraction, transport and magnetometry studies of their crystallographic, electronic and magnetic properties. The spectroscopic results are found to agree fairly closely with previously published experimental data on in situ grown thin films and cleaved single crystals. However, despite the higher photoelectron kinetic energies of the experiment, it has not been possible to observe 100% polarization at the Fermi level. Hence, our data do not support the claim of true half-metallicity for Fe(3)O(4).
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Affiliation(s)
- J G Tobin
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
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36
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Felser C, Fecher G, Balke B. Spintronik: eine Herausforderung für Materialwissenschaften und Festkörperchemie. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200601815] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Felser C, Fecher GH, Balke B. Spintronics: A Challenge for Materials Science and Solid-State Chemistry. Angew Chem Int Ed Engl 2007; 46:668-99. [PMID: 17219604 DOI: 10.1002/anie.200601815] [Citation(s) in RCA: 199] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Spintronics is a multidisciplinary field involving physics, chemistry, and engineering, and is a new research area for solid-state scientists. A variety of new materials must be found to satisfy different demands. The search for ferromagnetic semiconductors and stable half-metallic ferromagnets with Curie temperatures higher than room temperature remains a priority for solid-state chemistry. A general understanding of structure-property relationships is a necessary prerequisite for the design of new materials. In this Review, the most important developments in the field of spintronics are described from the point of view of materials science.
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Affiliation(s)
- Claudia Felser
- Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany.
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38
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Giazotto F, Taddei F, Beltram F, Fazio R. Crossed Andreev reflection-induced magnetoresistance. PHYSICAL REVIEW LETTERS 2006; 97:087001. [PMID: 17026324 DOI: 10.1103/physrevlett.97.087001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2005] [Indexed: 05/12/2023]
Abstract
We show that very large negative magnetoresistance can be obtained in magnetic trilayers in a current-in-plane geometry owing to the existence of crossed Andreev reflection. This spin valve consists of a thin superconducting film sandwiched between two ferromagnetic layers whose magnetization is allowed to be either parallelly or antiparallelly aligned. For a suitable choice of structure parameters and nearly fully spin-polarized ferromagnets, the magnetoresistance can exceed -80%. Our results are relevant for the design and implementation of spintronic devices exploiting ferromagnet-superconductor structures.
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40
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Kuhns PL, Hoch MJR, Reyes AP, Moulton WG, Wang L, Leighton C. Evolution with composition of the d-band density of states at the Fermi level in highly spin polarized Co1-xFexS2. PHYSICAL REVIEW LETTERS 2006; 96:167208. [PMID: 16712272 DOI: 10.1103/physrevlett.96.167208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2005] [Revised: 01/30/2006] [Indexed: 05/09/2023]
Abstract
Highly spin polarized (SP) and half-metallic ferromagnetic systems are of considerable current interest and of potential importance for spintronic applications. Recent work has demonstrated that Co1-xFexS2 is a highly polarized ferromagnet (FM) where the spin polarization can be tuned by alloy composition. Using 59Co FM-NMR as a probe, we have measured the low-temperature spin relaxation in this system in magnetic fields from 0 to 1.0 T for 0<or=x<or=0.3. The 59Co spin-lattice relaxation rates follow a linear T dependence. Analysis of the data, using expressions for a FM system, permits information to be obtained on the d-band density of states at the Fermi level. The results are compared with independent density of states values inferred from electronic specific heat measurements and band structure calculations. It is shown that FM-NMR can be an important method for investigating highly SP systems.
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Affiliation(s)
- P L Kuhns
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
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41
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Wang L, Umemoto K, Wentzcovitch RM, Chen TY, Chien CL, Checkelsky JG, Eckert JC, Dahlberg ED, Leighton C. Co1-xFexS2: a tunable source of highly spin-polarized electrons. PHYSICAL REVIEW LETTERS 2005; 94:056602. [PMID: 15783672 DOI: 10.1103/physrevlett.94.056602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Indexed: 05/24/2023]
Abstract
In the emerging field of spin-electronics ideal ferromagnetic electron sources would not only possess a high degree of spin polarization, but would also offer control over the magnitude of this polarization. We demonstrate here that a simple scheme can be utilized to control both the magnitude and the sign of the spin polarization of ferromagnetic CoS2, which we probe with a variety of techniques. The position of the Fermi level is fine-tuned by solid solution alloying with the isostructural diamagnetic semiconductor FeS2, leading to tunable spin polarization of up to 85%.
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Affiliation(s)
- L Wang
- Department of Chemical Engineering and Materials Science, University of Minnesota, USA
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Braden JG, Parker JS, Xiong P, Chun SH, Samarth N. Direct measurement of the spin polarization of the magnetic semiconductor (Ga,Mn)As. PHYSICAL REVIEW LETTERS 2003; 91:056602. [PMID: 12906617 DOI: 10.1103/physrevlett.91.056602] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2003] [Indexed: 05/24/2023]
Abstract
We have carried out a direct measurement of the degree of spin polarization (P) of the magnetic semiconductor Ga1-xMnxAs using Andreev reflection spectroscopy. Analyses of the conductance spectra of high transparency Ga(0.95)Mn(0.05)As/Ga junctions consistently yield an intrinsic value for P greater than 85%. Our experiments also revealed an extreme sensitivity of the measured spin polarization to the nature and quality of the interface for this material.
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Affiliation(s)
- J G Braden
- MARTECH and Department of Physics, Florida State University, Tallahassee, Florida 32306, USA
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Craco L, Laad MS, Müller-Hartmann E. Orbital Kondo effect in CrO2: a combined local-spin-density-approximation dynamical-mean-field-theory study. PHYSICAL REVIEW LETTERS 2003; 90:237203. [PMID: 12857287 DOI: 10.1103/physrevlett.90.237203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2002] [Indexed: 05/24/2023]
Abstract
Motivated by a collection of experimental results indicating the strongly correlated nature of the ferromagnetic metallic state of CrO2, we present results based on a combination of the actual band structure with dynamical-mean-field theory for the multiorbital case. In striking contrast to LSDA(+U) and model many-body approaches, much better semiquantitative agreement with (i) recent photoemission results, (ii) domain of applicability of the half-metal concept, and (iii) thermodynamic and dc transport data is obtained within a single picture. Our approach has broad applications for the detailed first-principles investigation of other transition metal oxide-based half-metallic ferromagnets.
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Affiliation(s)
- L Craco
- Institut für Theoretische Physik, Universität zu Köln, Zülpicher Strasse, 50937 Köln, Germany
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45
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Eschrig M, Kopu J, Cuevas JC, Schön G. Theory of half-metal/superconductor heterostructures. PHYSICAL REVIEW LETTERS 2003; 90:137003. [PMID: 12689318 DOI: 10.1103/physrevlett.90.137003] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2002] [Indexed: 05/24/2023]
Abstract
We investigate the Josephson coupling between two singlet superconductors separated by a half-metallic magnet. The mechanism behind the coupling is provided by the rotation of the quasiparticle spin in the superconductor during reflection events at the interface with the half metal. Spin rotation induces triplet correlations in the superconductor which, in the presence of surface spin-flip scattering, results in an indirect Josephson effect between the superconductors. We present a theory appropriate for studying this phenomenon and calculate physical properties for a superconductor/half-metal/superconductor heterostructure.
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Affiliation(s)
- M Eschrig
- Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe, Germany
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46
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Zhang Q, Nurmikko AV, Anguelouch A, Xiao G, Gupta A. Coherent magnetization rotation and phase control by ultrashort optical pulses in CrO(2) thin films. PHYSICAL REVIEW LETTERS 2002; 89:177402. [PMID: 12398704 DOI: 10.1103/physrevlett.89.177402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2001] [Indexed: 05/24/2023]
Abstract
We have applied photoexcitation by ultrashort laser pulses to single crystal thin CrO(2) films to trigger coherent transient magnetization rotation on a subnanosecond time scale, in macroscale single domains. Moreover, by applying the photoexcitation by pairs of temporally separated pump pulses, the transient precession of the magnetization can be phase controlled, depending on the time separation between the pulses. The mechanism behind the photoexcitation originates from the modulation of the magnetocrystalline anisotropy by nonthermal hot electron spins.
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Affiliation(s)
- Qiang Zhang
- Division of Engineering and Department of Physics, Brown University, Providence, Rhode Island 02912, USA
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47
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Xia K, Kelly PJ, Bauer GEW, Turek I. Spin-dependent transparency of ferromagnet/superconductor interfaces. PHYSICAL REVIEW LETTERS 2002; 89:166603. [PMID: 12398744 DOI: 10.1103/physrevlett.89.166603] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2002] [Indexed: 05/24/2023]
Abstract
We combine parameter-free calculations of the transmission and reflection matrices for clean and dirty interfaces with a scattering-theory formulation of Andreev reflection (AR) generalized to spin-polarized systems in order to critically evaluate the use of an extended Blonder-Tinkham-Klapwijk (BTK) model to extract values of the spin polarization for ferromagnetic metals from measurements of point-contact AR. Excellent agreement with the experimental conductance data is found for Pb/Cu but it is less good for Pb/Ni and poor for Pb/Co, indicating that the BTK formalism does not describe transport through superconducting/ferromagnetic interfaces correctly.
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Affiliation(s)
- K Xia
- Faculty of Applied Physics and MESA+ Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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48
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Biswas A, Fournier P, Qazilbash MM, Smolyaninova VN, Balci H, Greene RL. Evidence of a d- to s-wave pairing symmetry transition in the electron-doped cuprate superconductor Pr(2-x)CexCuO4. PHYSICAL REVIEW LETTERS 2002; 88:207004. [PMID: 12005593 DOI: 10.1103/physrevlett.88.207004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2001] [Indexed: 05/23/2023]
Abstract
We present point contact spectroscopy (PCS) data for junctions between a normal metal and the electron-doped cuprate superconductor Pr(2-x)CexCuO4 (PCCO). For the underdoped compositions of this cuprate ( x approximately 0.13) we observe a peak in the conductance-voltage characteristics of the point contact junctions. The shape and magnitude of this peak suggest the presence of Andreev bound states at the surface of underdoped PCCO which is evidence for a d-wave pairing symmetry. For overdoped PCCO ( x approximately 0.17) the PCS data do not show any evidence of Andreev bound states at the surface suggesting an s-wave pairing symmetry.
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Affiliation(s)
- Amlan Biswas
- Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland 20742
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49
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Goering E, Bayer A, Gold S, Schütz G, Rabe M, Rüdiger U, Güntherodt G. Strong anisotropy of projected 3d moments in epitaxial CrO2 films. PHYSICAL REVIEW LETTERS 2002; 88:207203. [PMID: 12005597 DOI: 10.1103/physrevlett.88.207203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2001] [Indexed: 05/23/2023]
Abstract
Soft x-ray magnetic circular dichroism (XMCD) spectra have been investigated for different crystallographic projections of CrO2. Strong anisotropic orbital Cr 3d contributions and a change of sign of the XMCD signal is observed and attributed to t(2g) majority states near the Fermi level. Additionally, moment analysis exhibits anisotropic behavior in the projected spin contributions of CrO2 assigned to a strong magnetic dipole term T(z), consistent with an intrinsic magnetic easy axis behavior along the CrO2 [001] axis. A reduced projected isotropic Cr 3d spin moment has been interpreted in terms of hybridization with oxygen.
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Affiliation(s)
- E Goering
- MPI für Metallforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany
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50
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Parker JS, Watts SM, Ivanov PG, Xiong P. Spin polarization of CrO2 at and across an artificial barrier. PHYSICAL REVIEW LETTERS 2002; 88:196601. [PMID: 12005656 DOI: 10.1103/physrevlett.88.196601] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2002] [Indexed: 05/23/2023]
Abstract
We report a systematic study of the spin polarization of epitaxial CrO2 films at and across an interface using planar junctions with a superconducting counterelectrode. By chemical modification of the CrO2 surface before the deposition of the superconductor, junctions with a wide range of barrier strength were obtained. Analysis of the conductance data on these junctions, especially under Zeeman splitting of the superconducting density of states, yields consistent, close to full spin polarization for CrO2 regardless of the barrier strength.
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Affiliation(s)
- J S Parker
- Department of Physics and Center for Materials Research and Technology (MARTECH), Florida State University, Tallahassee, Florida 32306, USA
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