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Kubota T, Shimada Y, Tsuchiya T, Yoshikawa T, Ito K, Takeda Y, Saitoh Y, Konno TJ, Kimura A, Takanashi K. Microstructures and Interface Magnetic Moments in Mn 2VAl/Fe Layered Films Showing Exchange Bias. NANOMATERIALS 2021; 11:nano11071723. [PMID: 34209025 PMCID: PMC8306298 DOI: 10.3390/nano11071723] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Revised: 06/23/2021] [Accepted: 06/25/2021] [Indexed: 11/22/2022]
Abstract
Heusler alloys are a material class exhibiting various magnetic properties, including antiferromagnetism. A typical application of antiferromagnets is exchange bias that is a shift of the magnetization curve observed in a layered structure consisting of antiferromagnetic and ferromagnetic films. In this study, a layered sample consisting of a Heusler alloy, Mn2VAl and a ferromagnet, Fe, is selected as a material system exhibiting exchange bias. Although the fully ordered Mn2VAl is known as a ferrimagnet, with an optimum fabrication condition for the Mn2VAl layer, the Mn2VAl/Fe layered structure exhibits exchange bias. The appearance of the antiferromagnetic property in the Mn2VAl is remarkable; however, the details have been unclear. To clarify the microscopic aspects on the crystal structures and magnetic moments around the Mn2VAl/Fe interface, cross-sectional scanning transmission electron microscope (STEM) observation, and synchrotron soft X-ray magnetic circular dichroism (XMCD) measurements were employed. The high-angle annular dark-field STEM images demonstrated clusters of Mn2VAl with the L21 phase distributed only around the interface to the Fe layer in the sample showing the exchange bias. Furthermore, antiferromagnetic coupling between the Mn- and Fe-moments were observed in element-specific hysteresis loops measured using the XMCD. The locally ordered L21 phase and antiferromagnetic Mn-moments in the Mn2VAl were suggested as important factors for the exchange bias.
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Affiliation(s)
- Takahide Kubota
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan; (Y.S.); (K.I.); (T.J.K.); (K.T.)
- Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
- Correspondence:
| | - Yusuke Shimada
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan; (Y.S.); (K.I.); (T.J.K.); (K.T.)
| | - Tomoki Tsuchiya
- Center for Science and Innovation in Spintronics, Core Research Cluster, Tohoku University, Sendai 980-8577, Japan;
| | - Tomoki Yoshikawa
- Graduate School of Science, Hiroshima University, Higashi-hiroshima 739-8526, Japan; (T.Y.); (A.K.)
| | - Keita Ito
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan; (Y.S.); (K.I.); (T.J.K.); (K.T.)
- Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
| | - Yukiharu Takeda
- Materials Sciences Research Center, Japan Atomic Energy Agency, Hyogo 679-5148, Japan; (Y.T.); (Y.S.)
| | - Yuji Saitoh
- Materials Sciences Research Center, Japan Atomic Energy Agency, Hyogo 679-5148, Japan; (Y.T.); (Y.S.)
| | - Toyohiko J. Konno
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan; (Y.S.); (K.I.); (T.J.K.); (K.T.)
| | - Akio Kimura
- Graduate School of Science, Hiroshima University, Higashi-hiroshima 739-8526, Japan; (T.Y.); (A.K.)
- Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-hiroshima 739-8526, Japan
| | - Koki Takanashi
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan; (Y.S.); (K.I.); (T.J.K.); (K.T.)
- Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
- Center for Science and Innovation in Spintronics, Core Research Cluster, Tohoku University, Sendai 980-8577, Japan;
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Fabrication of a novel magnetic topological heterostructure and temperature evolution of its massive Dirac cone. Nat Commun 2020; 11:4821. [PMID: 32973165 PMCID: PMC7515900 DOI: 10.1038/s41467-020-18645-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Accepted: 09/06/2020] [Indexed: 11/12/2022] Open
Abstract
Materials that possess nontrivial topology and magnetism is known to exhibit exotic quantum phenomena such as the quantum anomalous Hall effect. Here, we fabricate a novel magnetic topological heterostructure Mn4Bi2Te7/Bi2Te3 where multiple magnetic layers are inserted into the topmost quintuple layer of the original topological insulator Bi2Te3. A massive Dirac cone (DC) with a gap of 40–75 meV at 16 K is observed. By tracing the temperature evolution, this gap is shown to gradually decrease with increasing temperature and a blunt transition from a massive to a massless DC occurs around 200–250 K. Structural analysis shows that the samples also contain MnBi2Te4/Bi2Te3. Magnetic measurements show that there are two distinct Mn components in the system that corresponds to the two heterostructures; MnBi2Te4/Bi2Te3 is paramagnetic at 6 K while Mn4Bi2Te7/Bi2Te3 is ferromagnetic with a negative hysteresis (critical temperature ~20 K). This novel heterostructure is potentially important for future device applications. Magnetic topological heterostructures are promising devices to manipulate emergent quantum effects. Here, Hirahara et al. fabricate a novel magnetic topological heterostructure with a massive Dirac cone which becomes a massless one tuned by temperature.
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Bouravleuv AD, Lev LL, Piamonteze C, Wang X, Schmitt T, Khrebtov AI, Samsonenko YB, Kanski J, Cirlin GE, Strocov VN. Electronic structure of (In,Mn)As quantum dots buried in GaAs investigated by soft-x-ray ARPES. NANOTECHNOLOGY 2016; 27:425706. [PMID: 27631689 DOI: 10.1088/0957-4484/27/42/425706] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Electronic structure of a molecular beam epitaxy-grown system of (In,Mn)As quantum dots (QDs) buried in GaAs is explored with soft-x-ray angle-resolved photoelectron spectroscopy (ARPES) using photon energies around 1 keV. This technique, ideally suited for buried systems, extends the momentum-resolving capabilities of conventional ARPES with enhanced probing depth as well as elemental and chemical state specificity achieved with resonant photoexcitation. The experimental results resolve the dispersive energy bands of the GaAs substrate buried in ∼2 nm below the surface, and the impurity states (ISs) derived from the substitutional Mn atoms in the (In,Mn)As QDs and oxidized Mn atoms distributed near the surface. An energy shift of the Mn ISs in the QDs compared to (In,Mn)As DMS is attributed to the band offset and proximity effect at the interface with the surrounding GaAs. The absence of any ISs in the vicinity of the VBM relates the electron transport in (In,Mn)As QDs to the prototype (In,Mn)As diluted magnetic semiconductor. The SX-ARPES results are supported by measurements of the shallow core levels under variation of probing depth through photon energy. X-ray absorption measurements identify significant diffusion of interstitial Mn atoms out of the QDs towards the surface, and the role of magnetic circular dichroism is to block the ferromagnetic response of the (In,Mn)As QDs. Possible routes are drawn to tune the growth procedure aiming at practical applications of the (In,Mn)As based systems.
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Affiliation(s)
- A D Bouravleuv
- St.Petersburg Academic University RAS, 8-3 Khlopina st., 194021 St.Petersburg, Russia. Ioffe Physical Technical Institute RAS, 26 Politekhnicheskaya st., 194021 St.Petersburg, Russia. Institute for Analytical Instrumentation RAS, 31-33 Ivana Chernykh st., 190103 St.Petersburg, Russia. St.Petersburg State University, 7-9 Universitetskaya nab., 199034 St.Petersburg, Russia
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Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor Ge(1-x)Fex. Sci Rep 2016; 6:23295. [PMID: 26996202 PMCID: PMC4800415 DOI: 10.1038/srep23295] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 03/04/2016] [Indexed: 11/14/2022] Open
Abstract
We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, Ge1−xFex (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3d electrons are strongly hybridized with the Ge 4p states, and have a large orbital magnetic moment relative to the spin magnetic moment; i.e., morb/mspin ≈ 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20–100 K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature.
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Kobayashi M, Niwa H, Takeda Y, Fujimori A, Senba Y, Ohashi H, Tanaka A, Ohya S, Hai PN, Tanaka M, Harada Y, Oshima M. Electronic excitations of a magnetic impurity state in the diluted magnetic semiconductor (Ga,Mn)As. PHYSICAL REVIEW LETTERS 2014; 112:107203. [PMID: 24679325 DOI: 10.1103/physrevlett.112.107203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Indexed: 06/03/2023]
Abstract
The electronic structure of doped Mn in (Ga,Mn)As is studied by resonant inelastic x-ray scattering. From configuration-interaction cluster-model calculations, the line shapes of the Mn L3 resonant inelastic x-ray scattering spectra can be explained by d-d excitations from the Mn ground state dominated by charge-transferred states, in which hole carriers are bound to the Mn impurities, rather than a pure acceptor Mn2+ ground state. Unlike archetypical d-d excitation, the peak widths are broader than the experimental energy resolution. We attribute the broadening to a finite lifetime of the d-d excitations, which decay rapidly to electron-hole pairs in the host valence and conduction bands through the hybridization of the Mn 3d orbital with the ligand band.
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Affiliation(s)
- M Kobayashi
- Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan and Synchrotron Radiation Research Organization, The University of Tokyo, 1-490-2 Kouto, Sayo-cho, Tatsuno, Hyogo 679-5165, Japan
| | - H Niwa
- Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan and Synchrotron Radiation Research Organization, The University of Tokyo, 1-490-2 Kouto, Sayo-cho, Tatsuno, Hyogo 679-5165, Japan and Institute for Solid State Physics, The University of Tokyo, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan
| | - Y Takeda
- Quantum Beam Science Directorate, Japan Atomic Energy Agency, Sayo-gun, Hyogo 679-5148, Japan
| | - A Fujimori
- Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Y Senba
- Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo 679-5198, Japan
| | - H Ohashi
- Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo 679-5198, Japan
| | - A Tanaka
- Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
| | - S Ohya
- Department of Electronic Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - P N Hai
- Department of Electronic Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - M Tanaka
- Department of Electronic Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Y Harada
- Synchrotron Radiation Research Organization, The University of Tokyo, 1-490-2 Kouto, Sayo-cho, Tatsuno, Hyogo 679-5165, Japan and Institute for Solid State Physics, The University of Tokyo, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan
| | - M Oshima
- Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan and Synchrotron Radiation Research Organization, The University of Tokyo, 1-490-2 Kouto, Sayo-cho, Tatsuno, Hyogo 679-5165, Japan
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Saitoh Y, Fukuda Y, Takeda Y, Yamagami H, Takahashi S, Asano Y, Hara T, Shirasawa K, Takeuchi M, Tanaka T, Kitamura H. Performance upgrade in the JAEA actinide science beamline BL23SU at SPring-8 with a new twin-helical undulator. JOURNAL OF SYNCHROTRON RADIATION 2012; 19:388-93. [PMID: 22514174 PMCID: PMC3621280 DOI: 10.1107/s0909049512006772] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/17/2011] [Accepted: 02/15/2012] [Indexed: 05/31/2023]
Abstract
The soft X-ray beamline BL23SU at SPring-8 has undergone an upgrade with a twin-helical undulator of in-vacuum type to enhance the experimental capabilities of the endstations. The new light source with a fast helicity-switching operation allows not only the data throughput but also the sensitivity in X-ray magnetic circular dichroism (XMCD) to be improved. The operational performance and potential are described by presenting XMCD results of paramagnetic β-US(2) measured with a 10 T superconducting magnet.
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Affiliation(s)
- Yuji Saitoh
- Quantum Beam Science Directorate, Japan Atomic Energy Agency, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan.
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Dobrowolska M, Tivakornsasithorn K, Liu X, Furdyna JK, Berciu M, Yu KM, Walukiewicz W. Controlling the Curie temperature in (Ga,Mn)As through location of the Fermi level within the impurity band. NATURE MATERIALS 2012; 11:444-449. [PMID: 22344325 DOI: 10.1038/nmat3250] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Accepted: 01/18/2012] [Indexed: 05/31/2023]
Abstract
The ferromagnetic semiconductor (Ga,Mn)As has emerged as the most studied material for prototype applications in semiconductor spintronics. Because ferromagnetism in (Ga,Mn)As is hole-mediated, the nature of the hole states has direct and crucial bearing on its Curie temperature T(C). It is vigorously debated, however, whether holes in (Ga,Mn)As reside in the valence band or in an impurity band. Here we combine results of channelling experiments, which measure the concentrations both of Mn ions and of holes relevant to the ferromagnetic order, with magnetization, transport, and magneto-optical data to address this issue. Taken together, these measurements provide strong evidence that it is the location of the Fermi level within the impurity band that determines T(C) through determining the degree of hole localization. This finding differs drastically from the often accepted view that T(C) is controlled by valence band holes, thus opening new avenues for achieving higher values of T(C).
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Affiliation(s)
- M Dobrowolska
- Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA.
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Yamazaki Y, Kataoka T, Singh VR, Fujimori A, Chang FH, Huang DJ, Lin HJ, Chen CT, Ishikawa K, Zhang K, Kuroda S. Effect of co-doping of donor and acceptor impurities in the ferromagnetic semiconductor Zn(1-x)Cr(x)Te studied by soft x-ray magnetic circular dichroism. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:176002. [PMID: 21483085 DOI: 10.1088/0953-8984/23/17/176002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We have performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies of the diluted ferromagnetic semiconductor Zn(1-x)Cr(x)Te doped with iodine (I) or nitrogen (N), corresponding to electron or hole doping, respectively. From the shape of the Cr 2p absorption peak in the XAS spectra, it was concluded that the Cr ions in the undoped, I-doped and lightly N-doped samples are divalent (Cr(2+)), while Cr(2+) and trivalent (Cr(3+)) coexist in the heavily N-doped sample. This result indicates that the doped nitrogen atoms act as acceptors but that doped holes are located on the Cr ions. In the magnetic field dependence of the XMCD signal at the Cr 2p absorption edge, ferromagnetic behaviors were observed in the undoped, I-doped, and lightly N-doped samples, while ferromagnetism was considerably suppressed in the heavily N-doped sample, which is consistent with the results of magnetization measurements.
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Affiliation(s)
- Y Yamazaki
- Department of Physics, University of Tokyo, Tokyo 113-0033, Japan.
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Maccherozzi F, Sperl M, Panaccione G, Minár J, Polesya S, Ebert H, Wurstbauer U, Hochstrasser M, Rossi G, Woltersdorf G, Wegscheider W, Back CH. Evidence for a magnetic proximity effect up to room temperature at Fe/(Ga, Mn)As interfaces. PHYSICAL REVIEW LETTERS 2008; 101:267201. [PMID: 19113784 DOI: 10.1103/physrevlett.101.267201] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 09/30/2008] [Indexed: 05/27/2023]
Abstract
We report x-ray magnetic circular dichroism and superconducting quantum interference device magnetometry experiments to study magnetic order and coupling in thin Fe/(Ga, Mn)As(100) films. We observe induced magnetic order in the (Ga, Mn)As layer that extends over more than 2 nm, even at room temperature. We find spectroscopic evidences of a hybridized d configuration of Mn atoms in Fe/(Ga, Mn)As, with negligible Mn diffusion and/or MnFe intermixing. We show by experiment as well as by theory that the magnetic moment of the Mn ions couples antiparallel to the moment of the Fe overlayer.
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Affiliation(s)
- F Maccherozzi
- Laboratorio Nazionale TASC, INFM-CNR, in Area Science Park, S.S. 14, Km 163.5, I-34012, Trieste, Italy
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