Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P39: Magnetism and Spins in SemiconductorsFocus
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Sponsoring Units: GMAG DCMP DMP Chair: Yu-Sheng Ou, University of Delaware Room: BCEC 207 |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P39.00001: First-principles investigation of the magnetic transition in Fe-doped GaSb and InSb Hikari Shinya, Tetsuya Fukushima, Akira Masago, Kazunori Sato, Hiroshi Katayama-Yoshida Recently, Fe-doped semiconductors have been attracting much attention as ferromagnetic semiconductors due to the possibility of high Curie, fascinating functions such as low power consumption and high-speed operation, and fabrication of both n- and p-type. In this study, we have focused on GaSb and InSb as host semiconductors, and performed density functional theory calculations using the Korringa-Kohn-Rostoker Green’s function method with the coherent potential approximation (KKR-CPA). Our calculations reveal that, (Ga,Fe)Sb and (In,Fe)Sb show complex magnetic properties, which are determined by the correlation between magnetic exchange coupling constants and chemical pair interactions. Isoelectronic Fe-doped GaSb and InSb show strong antiferromagnetic interactions that originate from the super-exchange mechanism works between the Fe atoms. By modulating the chemical potentials–i.e., by n- or p-type doping–, the magnetic property can be changed drastically from antiferromagnetism to ferromagnetism, because the ferromagnetic double exchange mechanism becomes dominant. This transition can be well understood in terms of the Alexander-Anderson-Moriya mechanism. Our calculations indicate the possibility of manipulating (Ga,Fe)Sb and (In,Fe)Sb to achieve high Curie temperatures. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P39.00002: A multi-bands Hubbard model of intrinsic long range magnetic order in diluted magnetic semiconductors Weiyi Gong, Ching-Him Leung, Chuen-Keung Sin, Jingzhao Zhang, Xiaodong Zhang, Bin Xi, Junyi Zhu Recently, new long range ferromagnetic order has been discovered both experimentally and theoretically in carrier free semiconductor. However, there lacks quantitative model to explain the coupling mechanism that may extend to 7th nearest neighbors. In this work, we derived a multi-bands Hubbard model to explain the long range mechanism mediated by localized d states. Based on this model and combining with DFT calculations, we discovered a long range AFM order in DMS systems. Our model provides fundamental understandings of the new type of magnetic order in DMS. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P39.00003: Theoretical prediction of maximum Curie temperatures of Fe-based dilute magnetic semiconductors by first-principles calculations Hikari Shinya, Tetsuya Fukushima, Akira Masago, Kazunori Sato, Hiroshi Katayama-Yoshida Recently, Fe-based dilute magnetic semiconductors (DMSs), such as (In,Fe)As, (In,Fe)Sb and (Ga,Fe)Sb, have strongly attracted scientific and industrial attention, because of their high Curie temperatures and n-type carrier induced ferromagnetism. Several experiments showed that the ferromagnetic properties in Fe-based DMSs are strongly related to the inhomogeneous distribution of the Fe atoms, i.e., the Curie temperatures are modulated by the spinodal nano-decomposition, depending on crystal growth conditions. In this work, we predict the maximum Curie temperatures of the Fe-based DMSs with the spinodal nano-decomposition, on the basis of the Korringa-Kohn-Rostoker (KKR) Green’s function method within the density functional theory. The magnetic exchange coupling constants between the Fe atoms are calculated by the Liechtenstein’s formula, and then the Curie temperatures are estimated by the mean field approximation. It is found, from our calculations, that one can expect very high Curie temperatures beyond the room temperature in Fe-based DMSs, if the many Fe atoms gather together in the host semiconductor with keeping the zinc-blende structure and additional n- or p-type carriers are introduced. |
Wednesday, March 6, 2019 3:06PM - 3:42PM |
P39.00004: Element- and momentum-resolved electronic structure of the dilute magnetic semiconductor manganese doped gallium arsenide Invited Speaker: Slavomir Nemsak The dilute magnetic semiconductors have shown great promise in spin-based electronics applications due to their potential for ferromagnetic order at room temperature, and various unique switching and spin-dependent conductivity properties. However, the precise mechanism by which the transition-metal doping produces ferromagnetism has been controversial. We have studied a dilute magnetic semiconductor (5% manganese-doped gallium arsenide) with Bragg-reflection standing-wave hard X-ray angle-resolved photoemission spectroscopy (SW-HARPES), and resolved its electronic structure into element- and momentum- resolved components. The measured valence band intensities have been projected into element-resolved components using analogous photon energy scans of Ga 3d, Mn 2p, and As 3d core levels, with results in excellent agreement with element-projected Bloch spectral functions, further clarifying the electronic structure of this prototypical material. We will further discuss the capabilities of the SW-HARPES technique, which should be broadly applicable to other multi-element materials. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P39.00005: Ferromagnetic Stabilization of Eu-doped GaN Enhanced by Ga-vacancies Akira Masago, Hikari Shinya, Tetsuya Fukushima, Kazunori Sato, Hiroshi Katayama-Yoshida We report that the ferromagnetic states are stabilized by the double exchange interaction which enhanced by partially occupied N-2p hole band caused by Ga-vacancies in Eu-doped GaN, based on self-interaction-corrected (SIC) local density approximation. Eu-doped GaN is renowned for red light emitting diodes (LEDs), whereas it is interesting as a circular-polarized emission in the magnetic materials. In this study, we used a constant volume assumption and the coherent potential approximation (CPA) in the Korringa-Kohn-Rostoker (KKR) method with SIC. As a result, it indicates that electron-hole doping enhances the ferromagnetic states, because the dominant magnetic interaction is changed from Zener’s p-f exchange interaction to Zener’s double exchange interaction caused by the partially occupied N-2p band. In the enhancement, a major contribution to the magnetism is derived from the Ga-vacancies more than magnetic impurities Eu, which coupled with N anti-ferromagnetically. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P39.00006: Enhanced Optical Band Gap in Ultrathin Epitaxial Ferromagnetic Insulator GdN Films Gilvania Da Silva Vilela, Geetha Berera, Gregory Stephen, Xavier Gratens, Pavel Usachev, Don Heiman, Andre Henriques, Jagadeesh Moodera Full understanding of the optical and magnetic properties of insulating ferromagnetic GdN epitaxial ultrathin films would enable proximity coupling it to Graphene and 2D layer systems. Moreover, exchange split band of GdN acting as a spin-filter would offer the ideal means for spin polarized current injection in the above systems as well as into superconductors. With this objective we investigated the intrinsic magnetic and optical behavior of GdN films reactively rf sputtered in a UHV system under various conditions to optimize the high quality of films and reduce their defects. This in turn can enable GdN to achieve high spin filtering and the needed effective interfacial exchange interaction for 2D systems. In the range of film thickness (2 to 300nm, protected by AlN film) the dependence of direct and indirect band-gap energies as well as the ferromagnetic ordering temperature and magnetic moment was studied: optical gap increased while the magnetic moment reduced with film thickness reduction. |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P39.00007: Biaxial-stress driven tetragonal symmetry breaking in and high-temperature ferromagnetic semiconductor from half-metallic CrO2 Xiang-Bo Xiao, Bang-Gui Liu Here, we find through first-principles investigation that when a biaxial compressive stress is applied on rutile CrO2, the density of states at the Fermi level decreases with the in-plane compressive strain, there is a structural phase transition to an orthorhombic phase at the strain of -5.6%, and then appears an electronic phase transition to a semiconductor phase at -6.1%. Further analysis shows that this structural transition, accompanying the tetragonal symmetry breaking, is induced by the stress-driven distortion and rotation of the oxygen octahedron of Cr, and the half-metal-semiconductor transition originates from the enhancement of the crystal field splitting due to the structural change. Importantly, our systematic total-energy comparison indicates the ferromagnetic Curie temperature remains almost independent of the strain, near 400 K. This biaxial stress can be realized by applying biaxial pressure or growing the CrO2 epitaxially on appropriate substrates. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P39.00008: Design of Super-High-TChigh-entropy ferromagnetic semiconductors in Fe-doped III-V compound semiconductorsby spinodal nano-decomposition and volume compensated codoping Hikari Shinya, Tetsuya Fukushima, Akira Masago, Kazunori Sato, Hiroshi Katayama-Yoshida Based on the three general design rules of (1) the volume compensations [VC] by codoping, (2) spinodal nano-decomposition [SND], and (3) high-entropy ferromagnetic semiconductors [HEFS], we design the super-high-TC(TC> 1000K) HEFS in Fe-doped III-V compound semiconductors by computational nano-materials design. The substitutional(S) Fe impurity [Fe(S)] reduces the volume, whilethe interstitial (I = tetrahedral or octahedral site) Fe impurity [Fe(I)] expands the volume in III-V compound semiconductors, which is called volume compensation. The solubilitiesof the Fe(S) and Fe(I) are low due to the positive formation energy, so thatthe SND occurs due to the positive mixing energy. Based on the codoping of isoelectric Fe(S) and triple donors of Fe(I) more than 15~20%, we design the HEFS with super-high-TCbased on the strong ferromagnetic double exchange interactions in SND. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P39.00009: Interlayer Exchange Coupling Mediated by a Bulk Rashba Semiconductor Mahmoud Asmar, Wang Kong Tse Spin orbit coupling (SOC) in solids is a crucial ingredient in spintronic and magnetoelectronic phenomena. An example of SOC in solids is the 3D Rashba effect that arises in materials with broken inversion symmetry such as BiTeX (X=I,Cl and Br). These bismuth tellurohalides exhibit a giant Rashba coupling and are known as bulk Rashba semiconductors. In this talk, we present a RKKY theory for the interlayer exchange coupling in ferromagnet-BiTeX-ferromagnet trilayers. Due to the helical in-plane spin textures and associated Berry phase of the low-energy electrons, the interlayer exchange coupling as a function of layer thickness is found to exhibit unconventional dependence on the Rashba SOC. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P39.00010: Bias dependence of spin accumulation voltage in a non-degenerate Si spin valve SOOBEOM LEE, Fabien Rortais, Ryo Ohshima, Yuichiro Ando, Shinji Miwa, Yoshishige Suzuki, Hayato Koike, Masashi Shiraishi Si spintronics attracts great attention, and recent achievements in the field, such as the room temperature (RT) operation of spin MOSFET and the output spin voltage of more than 1 mV at RT due to the spin drift effect [1, 2], have been done by using non-degenerate (ND) Si. In the previous research [2], the spin voltages exhibited saturation under a high electric current (Iinj) injection regime, suggesting a possibility of modification of spin transport properties in the ND Si. Hence, we clarified the origin of the Iinj dependence of the spin signals in the ND Si in this study. The non-local 4-terminal measurement and the Hall measurement revealed that spin lifetime of the ND Si channel were independent of the Iinj at RT. Meanwhile, interface resistance of Fe/MgO/Si contact was reduced to the same order of spin resistance of the Si channel. A model calculation considering these results nicely reproduced the experimental Iinj dependence [3]. The detail will be discussed in the presentation. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P39.00011: Magnetotransport in InSb nanowires with ferromagnetic contacts Zedong Yang, Yifan Jiang, Diana Car, Sasa Gazibegovic, Paul Crowell, Sergey M Frolov, Erik P. A. M. Bakkers, Vlad S Pribiag InSb semiconductor nanowires are a promising and intensely-studied platform for investigating Majorana bound states [1]. Their strong spin-orbit coupling also makes them interesting for all-electrical control of single spins [2]. Moreover, owing to their relatively long mean free paths and quasi-one-dimensionality, InSb nanowires also have great potential for novel devices which could allow electrical control of spin currents. Motivated by these intriguing possibilities, we fabricated InSb nanowire devices with ferromagnetic contacts, which show evidence of ballistic transport. We report hysteretic features in the magneto-conductance measured at different back-gate voltages, and discuss the possible physical mechanisms responsible for these observations. |
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