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Wang XG, Guo GH, Dyrdał A, Barnaś J, Dugaev VK, Parkin SSP, Ernst A, Chotorlishvili L. Skyrmion Echo in a System of Interacting Skyrmions. Phys Rev Lett 2022; 129:126101. [PMID: 36179192 DOI: 10.1103/physrevlett.129.126101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 08/24/2022] [Accepted: 08/26/2022] [Indexed: 06/16/2023]
Abstract
We consider helical rotation of skyrmions confined in the potentials formed by nanodisks. Based on numerical and analytical calculations we propose the skyrmion echo phenomenon. The physical mechanism of the skyrmion echo formation is also proposed. Because of the distortion of the lattice, impurities, or pinning effect, confined skyrmions experience slightly different local fields, which leads to dephasing of the initial signal. The interaction between skyrmions also can contribute to the dephasing process. However, switching the magnetization direction in the nanodiscs (e.g., by spin transfer torque) also switches the helical rotation of the skyrmions from clockwise to anticlockwise (or vice versa), and this restores the initial signal (which is the essence of skyrmion echo).
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Affiliation(s)
- X-G Wang
- School of Physics and Electronics, Central South University, Changsha 410083, China
| | - Guang-Hua Guo
- School of Physics and Electronics, Central South University, Changsha 410083, China
| | - A Dyrdał
- Faculty of Physics, Adam Mickiewicz University, ul. Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
| | - J Barnaś
- Faculty of Physics, Adam Mickiewicz University, ul. Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
| | - V K Dugaev
- Department of Physics and Medical Engineering, Rzeszów University of Technology, 35-959 Rzeszów, Poland
| | - S S P Parkin
- Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany
| | - A Ernst
- Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany
- Institute for Theoretical Physics, Johannes Kepler University, Altenberger Straße 69, 4040 Linz, Austria
- Donostia International Physics Center (DIPC), 20018 Donostia-San Sebastián, Basque Country, Spain
| | - L Chotorlishvili
- Department of Physics and Medical Engineering, Rzeszów University of Technology, 35-959 Rzeszów, Poland
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2
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Wang XG, Chotorlishvili L, Arnold N, Dugaev VK, Maznichenko I, Barnaś J, Buczek PA, Parkin SSP, Ernst A. Plasmonic Skyrmion Lattice Based on the Magnetoelectric Effect. Phys Rev Lett 2020; 125:227201. [PMID: 33315433 DOI: 10.1103/physrevlett.125.227201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 08/04/2020] [Accepted: 10/01/2020] [Indexed: 06/12/2023]
Abstract
The physical mechanism of the plasmonic skyrmion lattice formation in a magnetic layer deposited on a metallic substrate is studied theoretically. The optical lattice is the essence of the standing interference pattern of the surface plasmon polaritons created through coherent or incoherent laser sources. The nodal points of the interference pattern play the role of lattice sites where skyrmions are confined. The confinement appears as a result of the magnetoelectric effect and the electric field associated with the plasmon waves. The proposed model is applicable to yttrium iron garnet and single-phase multiferroics and combines plasmonics and skyrmionics.
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Affiliation(s)
- X-G Wang
- School of Physics and Electronics, Central South University, Changsha 410083, China
| | - L Chotorlishvili
- Institut für Physik, Martin-Luther Universität Halle-Wittenberg, D-06120 Halle/Saale, Germany
| | - N Arnold
- Soft Materials Lab, Linz Institute of Technology LIT, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria
| | - V K Dugaev
- Department of Physics and Medical Engineering, Rzeszów University of Technology, 35-959 Rzeszów, Poland
| | - I Maznichenko
- Institut für Physik, Martin-Luther Universität Halle-Wittenberg, D-06120 Halle/Saale, Germany
| | - J Barnaś
- Faculty of Physics, Adam Mickiewicz University, ul. Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
- Institute of Molecular Physics, Polish Academy of Sciences, ul. M. Smoluchowskiego 17, 60-179 Poznańn, Poland
| | - P A Buczek
- Department of Engineering and Computer Sciences, Hamburg University of Applied Sciences, Berliner Tor 7, 20099 Hamburg, Germany
| | - S S P Parkin
- Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany
| | - A Ernst
- Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany
- Institute for Theoretical Physics, Johannes Kepler University, Altenberger Straße 69, 4040 Linz, Austria
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Dyrdał A, Barnaś J, Fert A. Spin-Momentum-Locking Inhomogeneities as a Source of Bilinear Magnetoresistance in Topological Insulators. Phys Rev Lett 2020; 124:046802. [PMID: 32058752 DOI: 10.1103/physrevlett.124.046802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2019] [Revised: 12/15/2019] [Indexed: 06/10/2023]
Abstract
A new mechanism of bilinear magnetoresistance (BMR) is proposed and studied theoretically within the minimal model describing surface electronic states in topological insulators. The BMR appears as a consequence of the second-order response to electric field, and depends linearly on both magnetic field and current (electric field). The mechanism is based on the interplay of current-induced spin polarization and scattering processes due to inhomogeneities of spin-momentum locking, that unavoidably appear as a result of structural defects in topological insulators. The proposed mechanism leads to the BMR even if the electronic band structure is isotropic (e.g., absence of hexagonal warping), and is shown to be dominant at lower Fermi energies.
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Affiliation(s)
- A Dyrdał
- Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
- Institut für Physik, Martin-Luther-Universität HalleWittenberg, 06099 Halle (Saale), Germany
| | - J Barnaś
- Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
| | - A Fert
- Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, 91767 Palaiseau, France
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Tepper J, Barnaś J. Klein tunnelling and Hartman effect in graphene junctions with proximity exchange field. J Phys Condens Matter 2019; 31:225302. [PMID: 30812020 DOI: 10.1088/1361-648x/ab0b20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Tunnelling of electrons in graphene-based junctions is studied theoretically. Graphene is assumed to be deposited either directly on a ferromagnetic insulator or on a few atomic layers of boron nitride which separate graphene from a metallic ferromagnetic substrate. Such junctions can be formed by appropriate external gating of the corresponding system. To describe low-energy electronic states near the Dirac points, certain effective Hamiltonians available in the relevant literature are used. These Hamiltonians include staggered potential and exchange interaction due to ferromagnetic substrates. Tunnelling in the systems under consideration is then spin-dependent. The main focus is on Klein tunnelling and also on the group delay and the associated Hartman effect. The impact of a gap induced in the spectrum at the Dirac points on tunnelling is analysed in detail.
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Affiliation(s)
- J Tepper
- Faculty of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland
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Zberecki K, Wierzbicki M, Swirkowicz R, Barnaś J. Unique magnetic and thermoelectric properties of chemically functionalized narrow carbon polymers. J Phys Condens Matter 2017; 29:045303. [PMID: 27882898 DOI: 10.1088/1361-648x/29/4/045303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We analyze magnetic, transport and thermoelectric properties of narrow carbon polymers, which are chemically functionalized with nitroxide groups. Numerical calculations of the electronic band structure and the corresponding transmission function are based on density functional theory. Transport and thermoelectric parameters are calculated in the linear response regime, with particular interest in charge and spin thermopowers (charge and spin Seebeck effects). Such nanoribbons are shown to have thermoelectric properties described by large thermoelectric efficiency, which makes these materials promising from the application point of view.
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Affiliation(s)
- K Zberecki
- Faculty of Physics, Warsaw University of Technology,ul. Koszykowa 75, 00-662 Warsaw, Poland
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Zberecki K, Swirkowicz R, Wierzbicki M, Barnaś J. Spectacular enhancement of thermoelectric phenomena in chemically synthesized graphene nanoribbons with substitution atoms. Phys Chem Chem Phys 2016; 18:18246-54. [PMID: 27331357 DOI: 10.1039/c6cp02877b] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We analyze theoretically the transport and thermoelectric properties of graphene nanoribbons of a specific geometry, which have been synthesized recently from polymers [Cai, et al., Nature, 2011, 466, 470]. When such nanoribbons are modified at one of the two edges by Al or N substitutions, they acquire a ferromagnetic moment localized at the modified edge. We present numerical results on the electronic structure and thermoelectric properties (including also spin thermoelectricity) of the modified nanoribbons. The results show that such nanoribbons can display large thermoelectric efficiency in certain regions of chemical potential, where the corresponding electric and spin figures of merit achieve unusually large values. The enhancement of thermoelectric efficiency follows from a reduced phonon heat conductance of the nanoribbons and from their peculiar electronic band structure. Thus, such nanoribbons are promising for practical applications in nanoelectronic and spintronic devices.
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Affiliation(s)
- K Zberecki
- Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, 00-662 Warsaw, Poland.
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Abstract
We present a tight binding description of electronic properties of the interface between LaAlO3 (LAO) and SrTiO3 (STO). The description assumes LAO and STO perovskites as sets of atomic layers in the x-y plane, which are weakly coupled by an interlayer hopping term along the z axis. The interface is described by an additional potential, U0, which simulates a planar defect. Physically, the interfacial potential can result from either a mechanical stress at the interface or other structural imperfections. We show that depending on the potential strength, charge carriers (electrons or holes) may form an energy band which is localized at the interface and is within the band gaps of the constitutent materials (LAO and STO). Moreover, our description predicts a valve effect at a certain critical potential strength, U0cr, when the interface potential works as a valve suppressing the interfacial conductivity. In other words, the interfacial electrons become dispersionless at U0 = U0cr, and thus cannot propagate. This critical value separates the quasielectron (U0 < U0cr) and quasihole (U0 > U0cr) regimes of the interfacial conductivity.
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Affiliation(s)
- V A Stephanovich
- Institute of Physics, Opole University, ul. Oleska 48, 45-052 Opole, Poland.
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8
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Zberecki K, Swirkowicz R, Wierzbicki M, Barnaś J. Enhanced thermoelectric efficiency in ferromagnetic silicene nanoribbons terminated with hydrogen atoms. Phys Chem Chem Phys 2015; 16:12900-8. [PMID: 24848750 DOI: 10.1039/c4cp01039f] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using ab initio methods we calculate thermoelectric and spin thermoelectric properties of silicene nanoribbons with bare, mono-hydrogenated and di-hydrogenated edges. Asymmetric structures, in which one edge is either bare or di-hydrogenated while the other edge is mono-hydrogenated (0H-1H and 2H-1H nanoribbons), have a ferromagnetic ground state and display remarkable conventional and spin thermoelectric properties. Strong enhancement of the thermoelectric efficiency, both conventional and spin ones, results from a very specific band structure of such nanoribbons, where one spin channel is blocked due to an energy gap while the other spin channel is highly conductive. In turn, 0H-2H and 2H-2H nanoribbons (with one edge being either bare or di-hydrogenated and the other edge being di-hydrogenated) are antiferromagnetic in the ground state. Accordingly, the corresponding spin channels are equivalent, and only conventional thermoelectric effects can occur in these nanoribbons.
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Affiliation(s)
- K Zberecki
- Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, 00-662 Warsaw, Poland.
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Abstract
Using ab initio methods we calculate the thermoelectric and spin thermoelectric properties of zigzag SiC nanoribbons, asymmetrically terminated with hydrogen. Such nanoribbons display a ferromagnetic ground state, with edge magnetic moments oriented in parallel. Both thermopower and spin thermopower have been determined as a function of chemical potential and temperature. To find the thermoelectric efficiency, the total heat conductance has been calculated, i.e. the electronic and phonon contributions. Numerical results for SiC nanoribbons are compared with those for graphene and silicene ones.
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Affiliation(s)
- K Zberecki
- Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, 00-662 Warsaw, Poland.
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10
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Abstract
Conventional and spin related thermoelectric effects in zigzag boron nitride nanoribbons are studied theoretically within the Density Functional Theory (DFT) approach.
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Affiliation(s)
- K. Zberecki
- Faculty of Physics
- Warsaw University of Technology
- 00-662 Warsaw
- Poland
| | - R. Swirkowicz
- Faculty of Physics
- Warsaw University of Technology
- 00-662 Warsaw
- Poland
| | - J. Barnaś
- Faculty of Physics
- Adam Mickiewicz University
- 61-614 Poznań
- Poland
- Institute of Molecular Physics
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11
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Karwacki L, Trocha P, Barnaś J. Spin-dependent thermoelectric properties of a Kondo-correlated quantum dot with Rashba spin-orbit coupling. J Phys Condens Matter 2013; 25:505305. [PMID: 24275387 DOI: 10.1088/0953-8984/25/50/505305] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Thermoelectric transport phenomena in a single-level quantum dot coupled to ferromagnetic leads are considered theoretically in the Kondo regime. The dot is described by the Anderson model with Rashba type spin-orbit interactions. The finite-U mean field slave boson technique is used to describe transport characteristics, such as the heat conductance, thermopower and thermoelectric efficiency (figure of merit). The role of quantum interference effects in the thermoelectric parameters is also analyzed.
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Affiliation(s)
- L Karwacki
- Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
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12
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Abstract
We study the spin-resolved transport through single-level quantum dots strongly coupled to ferromagnetic leads in the Kondo regime, with a focus on contact and material asymmetry-related effects. By using the numerical renormalization group method, we analyze the dependence of relevant spectral functions, the linear conductance and the tunnel magnetoresistance on the system asymmetry parameters. In the parallel magnetic configuration of the device the Kondo effect is generally suppressed due to the presence of an exchange field, irrespective of the system's asymmetry. In the antiparallel configuration, on the other hand, the Kondo effect can develop if the system is symmetric. We show that even relatively weak asymmetry may lead to suppression of the Kondo resonance in the antiparallel configuration and thus give rise to nontrivial behavior of the tunnel magnetoresistance. In addition, by using the second-order perturbation theory we derive general formulas for the exchange field in both magnetic configurations of the system.
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Affiliation(s)
- K P Wójcik
- Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
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13
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Dugaev VK, Inglot M, Sherman EY, Berakdar J, Barnaś J. Nonlinear anomalous Hall effect and negative magnetoresistance in a system with random Rashba field. Phys Rev Lett 2012; 109:206601. [PMID: 23215513 DOI: 10.1103/physrevlett.109.206601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2012] [Indexed: 06/01/2023]
Abstract
We predict two spin-dependent transport phenomena in two-dimensional electron systems, which are induced by a spatially fluctuating Rashba spin-orbit interaction. When the electron gas is magnetized, the random Rashba interaction leads to the anomalous Hall effect. An example of such a system is a narrow-gap magnetic semiconductor-based symmetric quantum well. We show that the anomalous Hall conductivity reveals a strongly nonlinear dependence on the magnetization, decreasing exponentially at large spin density. We also show that electron scattering from a fluctuating Rashba field in a two-dimensional nonmagnetic electron system leads to a negative magnetoresistance arising solely due to spin-dependent effects.
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Affiliation(s)
- V K Dugaev
- Department of Physics, Rzeszów University of Technology, al. Powstańców Warszawy 6, 35-959 Rzeszów, Poland
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14
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Abstract
We analyze theoretically transport properties of graphene quantum dots weakly coupled to normal and ferromagnetic leads. The calculations are performed by using the real-time diagrammatic technique in the first-order approximation with respect to tunneling processes. First, we analyze the energy spectrum of graphene dots of different shape. Then, we determine the current flowing through the system and the differential conductance. We show that the structure of the Coulomb diamonds of graphene quantum dots greatly depends on energy spectrum and therefore on the shape of the dots. In the case of ferromagnetic leads we also determine the tunnel magnetoresistance, which displays a nontrivial behavior depending on the number of charge states taking part in transport, and on particular shape of the graphene flake.
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Affiliation(s)
- I Weymann
- Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
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15
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Cascales JP, Herranz D, Aliev FG, Szczepański T, Dugaev VK, Barnaś J, Duluard A, Hehn M, Tiusan C. Controlling shot noise in double-barrier magnetic tunnel junctions. Phys Rev Lett 2012; 109:066601. [PMID: 23006290 DOI: 10.1103/physrevlett.109.066601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Revised: 05/30/2012] [Indexed: 06/01/2023]
Abstract
We demonstrate that shot noise in Fe/MgO/Fe/MgO/Fe double-barrier magnetic tunnel junctions is determined by the relative magnetic configuration of the junction and also by the asymmetry of the barriers. The proposed theoretical model, based on sequential tunneling through the system and including spin relaxation, successfully accounts for the experimental observations for bias voltages below 0.5 V, where the influence of quantum well states is negligible. A weak enhancement of conductance and shot noise, observed at some voltages (especially above 0.5 V), indicates the formation of quantum well states in the middle magnetic layer. The observed results open up new perspectives for a reliable magnetic control of the most fundamental noise in spintronic structures.
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Affiliation(s)
- J P Cascales
- Departmento Fisica Materia Condensada, Universidad Autonoma de Madrid, 28049 Madrid, Spain
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Dyrdał A, Barnaś J. Intrinsic contribution to spin Hall and spin Nernst effects in a bilayer graphene. J Phys Condens Matter 2012; 24:275302. [PMID: 22713801 DOI: 10.1088/0953-8984/24/27/275302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We consider intrinsic contributions to the spin Hall and spin Nernst effects in a bilayer graphene. The relevant electronic spectrum is obtained from the tight binding Hamiltonian, which also includes the intrinsic spin-orbit interaction. The corresponding spin Hall and spin Nernst conductivities are compared with those obtained from effective low-energy k ⋅p and reduced Hamiltonians, which are appropriate for states in the vicinity of the Fermi level of a neutral bilayer graphene. Both conductivities are determined within the linear response theory and Green function formalism. The influence of an external voltage between the two atomic sheets is also considered. The results reveal a transition from the topological spin Hall insulator phase at low voltages to conventional insulator phase at larger voltages.
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Affiliation(s)
- A Dyrdał
- Faculty of Physics, Adam Mickiewicz University, ulica Umultowska 85, 61-614 Poznań, Poland.
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Herranz D, Aliev FG, Tiusan C, Hehn M, Dugaev VK, Barnaś J. Tunneling in double barrier junctions with "hot spots". Phys Rev Lett 2010; 105:047207. [PMID: 20867883 DOI: 10.1103/physrevlett.105.047207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Indexed: 05/29/2023]
Abstract
We investigate electronic transport in epitaxial Fe(100)/MgO/Fe/MgO/Fe double magnetic tunnel junctions with soft barrier breakdown (hot spots). Specificity of these junctions is continuous middle layer and nitrogen doping of the MgO barriers which provides soft breakdown at biases about 0.5 V. In the junctions with hot spots we observe quasiperiodic changes in the resistance as a function of bias voltage which point out formation of quantum well states in the middle Fe continuous free layer. The room-temperature oscillations have been observed in both parallel and antiparallel magnetic configurations and for both bias polarizations. A simple model of tunneling through hot spots in the double barrier magnetic junction is proposed to qualitatively explain this effect.
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Affiliation(s)
- D Herranz
- Departamento Física Materia Condensada, Universidad Autónoma de Madrid, 28049, Madrid, Spain
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18
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Dugaev VK, Bruno P, Barnaś J. Comment on "Weak localization in ferromagnetic (Ga,Mn)As nanostructures". Phys Rev Lett 2008; 101:129701-129702. [PMID: 18851420 DOI: 10.1103/physrevlett.101.129701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2008] [Indexed: 05/26/2023]
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Gmitra M, Barnaś J. Thermally assisted current-driven bistable precessional regimes in asymmetric spin valves. Phys Rev Lett 2007; 99:097205. [PMID: 17931033 DOI: 10.1103/physrevlett.99.097205] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2007] [Indexed: 05/25/2023]
Abstract
Spin-transfer torque in asymmetric spin valves can destabilize both parallel and antiparallel configurations and can lead to precessional modes also in the absence of an external magnetic field. We find a bistable precessional regime in such systems and show that thermal fluctuations can excite transitions (telegraph noise) between the corresponding oscillatory regimes that are well separated by irreversible paths at low temperatures. Because of the thermally induced transitions, the frequency of the resulting current-driven oscillations is different from that obtained at very low temperatures. We also show that the power spectrum in the bistable region is dominated by the out-of-plane oscillatory mode.
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Affiliation(s)
- M Gmitra
- Institute of Physics, P.J. Safárik University, Park Angelinum 9, 040 01 Kosice, Slovak Republic
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Gmitra M, Barnaś J. Current-driven destabilization of both collinear configurations in asymmetric spin valves. Phys Rev Lett 2006; 96:207205. [PMID: 16803203 DOI: 10.1103/physrevlett.96.207205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2006] [Indexed: 05/10/2023]
Abstract
Spin-transfer torque in spin valves usually destabilizes one of the collinear configurations (either parallel or antiparallel) and stabilizes the second one. Apart from this, balance of the spin-transfer and damping torques can lead to steady precessional modes. In this Letter we show that in some asymmetric nanopillars, spin current can destabilize both parallel and antiparallel configurations. As a result, stationary precessional modes can occur at zero magnetic field. The corresponding phase diagram as well as frequencies of the precessional modes have been calculated in the framework of macrospin model. The relevant spin-transfer torque has been calculated in terms of the macroscopic model based on spin diffusion equations.
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Affiliation(s)
- M Gmitra
- Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland
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Dugaev VK, Berakdar J, Barnaś J. Tunable conductance of magnetic nanowires with structured domain walls. Phys Rev Lett 2006; 96:047208. [PMID: 16486888 DOI: 10.1103/physrevlett.96.047208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2005] [Indexed: 05/06/2023]
Abstract
We show that in a magnetic nanowire with double magnetic domain walls, quantum interference results in spin-split quasistationary states localized mainly between the domain walls. Spin-flip-assisted transmission through the domain structure increases strongly when these size-quantized states are tuned on resonance with the Fermi energy, e.g., upon varying the distance between the domain walls which results in resonance-type peaks of the wire conductance. This novel phenomenon is shown to be utilizable to manipulate the spin density in the domain vicinity. The domain wall parameters are readily controllable, and the predicted effect is hence exploitable in spintronic devices.
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Affiliation(s)
- V K Dugaev
- Departamento de Física and CFIF, Instituto Superior Técnico, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal
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Dugaev V, Berakdar J, Barnaś J, Dobrowolski W, Mitin V, Vieira M. Magnetoresistance due to domain walls in semiconducting magnetic nanostructures. Materials Science and Engineering: C 2005. [DOI: 10.1016/j.msec.2005.06.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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23
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Martinek J, Sindel M, Borda L, Barnaś J, König J, Schön G, von Delft J. Kondo effect in the presence of itinerant-electron ferromagnetism studied with the numerical renormalization group method. Phys Rev Lett 2003; 91:247202. [PMID: 14683152 DOI: 10.1103/physrevlett.91.247202] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2003] [Indexed: 05/24/2023]
Abstract
The Kondo effect in quantum dots (QDs)-artificial magnetic impurities-attached to ferromagnetic leads is studied with the numerical renormalization group method. It is shown that the QD level is spin split due to the presence of ferromagnetic electrodes, leading to a suppression of the Kondo effect. We find that the Kondo effect can be restored by compensating this splitting with a magnetic field. Although the resulting Kondo resonance then has an unusual spin asymmetry with a reduced Kondo temperature, the ground state is still a locally screened state, describable by Fermi liquid theory and a generalized Friedel sum rule, and transport at zero temperature is spin independent.
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Affiliation(s)
- J Martinek
- Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe, Germany
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Martinek J, Utsumi Y, Imamura H, Barnaś J, Maekawa S, König J, Schön G. Kondo effect in quantum dots coupled to ferromagnetic leads. Phys Rev Lett 2003; 91:127203. [PMID: 14525397 DOI: 10.1103/physrevlett.91.127203] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2002] [Indexed: 05/24/2023]
Abstract
We study the Kondo effect in a quantum dot coupled to ferromagnetic leads and analyze its properties as a function of the spin polarization of the leads. Based on a scaling approach, we predict that for parallel alignment of the magnetizations in the leads the strong-coupling limit of the Kondo effect is reached at a finite value of the magnetic field. Using an equation of motion technique, we study nonlinear transport through the dot. For parallel alignment, the zero-bias anomaly may be split even in the absence of an external magnetic field. For antiparallel spin alignment and symmetric coupling, the peak is split only in the presence of a magnetic field, but shows a characteristic asymmetry in amplitude and position.
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Affiliation(s)
- J Martinek
- Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe, Germany
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