Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K21: Magnetic Semiconductors: Materials and PropertiesFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Giti Khodaparast, Virginia Tech Room: LACC 309 |
Wednesday, March 7, 2018 8:00AM - 8:36AM |
K21.00001: Control of Magnetic Properties of (Ga,Mn)As and GaAs-Compatible Ferromagnetic Heterostructures Invited Speaker: Jianhua Zhao Magnetic semiconductors and ferromagnet/semiconductor heterostructures are two promising material systems for manipulating the spin degree of freedom of charge carriers in semiconductors to merge functionalities of information storage, logic and communications into one chip. In this talk, I shall first present our recent work on robust modulation of magnetism in (Ga,Mn)As [1,2], a prototypical member of the family of magnetic semiconductors. We realized giant modulation of the magnetism, including complete demagnetization of ferromagnetism, in (Ga,Mn)As via electric field with the assistance of a special dielectric, ionic liquid or solid state ionic gel [3]. I shall then describe the MBE growth and characterizations of several ferromagnet/semiconductor heterostructures, featuring the GaAs-compatible Mn-based binary alloy films with large perpendicular magnetic anisotropy (PMA) [4,5]. I shall provide the three electrical transport features which support the presence of the orbital two-channel Kondo effect in epitaxial L10-MnAl film with PMA [6,7]. Finally, I shall show the observation of well-defined tunneling magnetic resistance of L10-MnGa based perpendicularly magnetic tunnel junctions [8]. |
Wednesday, March 7, 2018 8:36AM - 8:48AM |
K21.00002: Coherent Acoustic Phonon Generation in Ferromagnetic GaMnAs Films Brenden Magill, Giti Khodaparast, Gary Sanders, Christopher Stanton, Joshua Holleman, Stephen McGill, Hiro Munekata Ferromagnetic semiconductors such GaMnAs exhibit strong coupling between their magnetic and elastic properties. This allows their magnetic anisotropy to be manipulated by applying external strain, electric or magnetic fields, as well as optical fields. In this talk, we report on the ultrafast optical processes in ferromagnetic (III,Mn)V semiconductor films induced by femtosecond laser pulses. We present two-color time-resolved spectroscopy on MBE grown GaMnAs (TC = 110 K). These measurements allow us to observe coherent phonon dynamics. Here we focus on the generation of coherent acoustic phonon wavepackets, between 40.9 – 42.9 GHz, which are generated in the ferromagnetic layer which display strong tunability in the presence of external magnetic fields. We compare our experimental observations to theoretical calculations on an effective mass approximation, using an eight-band Pidgeon-Brown model to calculate magnetic field induced changes to the electronic structure, absorption and index of refraction, and coherent phonon amplitude. |
Wednesday, March 7, 2018 8:48AM - 9:00AM |
K21.00003: Effects on Ferromagnetic Properties of GaMnAs Induced by Proximity of Topological Insulator Bi2Se3 Seul-Ki Bac, Hakjoon Lee, Sangyeop Lee, Seonghoon Choi, Sanghoon Lee, Xinyu Liu, Malgorzata Dobrowolska, J Furdyna We report the observation of significant changes in magnetic properties of the ferromagnetic semiconductor GaMnAs induced by the proximity of a Bi2Se3 layer integrated with the GaMnAs film. Bi2Se3/GaMnAs bilayer used in this investigation was grown by molecular beam epitaxy on (001) GaAs substrates and investigated via magnetotransport experiments. In order to identify the effect of Bi2Se3 on the magnetic properties of GaMnAs, the Bi2Se3 was removed from half of the specimen. This etching process leaves GaMnAs layer serving as a reference. All measurements were carried out simultaneously on the bilayer and the control specimen. The bilayer and the control layer show several different properties, as follows: 1) The GaMnAs in the bilayer was noticeably more metallic than the control layer. 2) The Curie temperature of GaMnAs in the bilayer was significantly higher than that of the control GaMnAs layer. 3) The GaMnAs layer in the bilayer shown much larger coercive fields than the control GaMnAs layer in in-plane magnetization reversal process owing to a strong admixture of cubic magnetocrystalline anisotropy observed in that layer. We ascribe the observed phenomena to proximity effects arising from the presence of the interface between the two materials. |
Wednesday, March 7, 2018 9:00AM - 9:12AM |
K21.00004: Evidence for Magnetic Polarons in EuB6 from Small Angle Neutron Scattering Gabrielle Beaudin, Andrea Bianchi, Alexandre Désilets-Benoit, Mark Laver, Robert Arnold, Stravos Samothrakitis, Michel Kenzelmann, Simon Gerber, Jorge Gavilano, Charles Dewhust, Robert Cubitt We present results of small-angle neutron scattering (SANS) experiments on the rare-earth, magnetic semiconductor EuB6. This compound exhibits two phase transitions: Upon cooling from an insulating state at high temperature, it first becomes metallic with a drop at a TM of 14.5 K, after which it orders ferromagnetically with a TC of 11.8 K. We carried out SANS experiments over a large range of scattering wave vectors q from 0.006 to 0.140 Å-1 and temperatures from 2 to 60 K. The experiments show a Lorentzian dependence on the wave vector in the magnetic scattering intensity for temperatures just above TC , which demonstrates the presence of magnetic polarons. Below TC, the polarons merge together, and most of the observed intensity is, as indicated by a q dependence, from scattering of ferromagnetic wall domains. We calculated a correlation length from this Lorentzian fit and obtained a range of 10 to 100 Å for the size of the magnetic polarons. We also applied magnetic fields from zero to 500 mT to the system. This pushes the formation of magnetic polarons to higher temperatures: 22 K for 250 mT, and 24 K for 500 mT, as measured by the integrated magnetic intensity averaged over the q-range from 0.006 to 0.140 Å-1. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K21.00005: Light Switching of the Ferromagnetic Phase in the Magnetic Semiconductor EuSe Andre Henriques, Pavel Usachev, Alexander Naupa, Xavier Gratens, Valmir Chitta, Gunther Springholz We demonstrate that light resonant with the EuSe bandgap forces the crystal lattice spins into complete ferromagnetic alignment, due to the generation of magnetic polarons. The magnetic polaron has a super gigantic magnetic moment approaching 6000 Bohr magnetons, which is an absolute record value, and more than two orders of magnitude larger than for polarons seen in diluted magnetic semiconductors. Hence a magnetic field of only 8mT is sufficient to fully align all polarons. The polaron is described by an effective exchange magnetic field of about 1 Tesla. This field is sufficient to drive the paramagnetic lattice into the ferromagnetic state. A self-consistent quantum-mechanical calculation of the magnetic polaron in EuSe supports the experimental findings. It also provides a clear-cut picture of the magnetic polaron inner spin structure, such as the radial distribution of spin orientation and exchange magnetic field. |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K21.00006: Microscopic origin of ferromagnetism in Fe-doped III-V semiconductors Hikari Shinya, Tetsuya Fukushima, Akira Masago, Kazunori Sato, Hiroshi Katayama-Yoshida Recently, Fe-doped III-V type semiconductors have attracted much attention due to the following two reasons. (i) (In,Fe)Sb and (Ga,Fe)Sb possess the room temperature ferromagnetism. (ii) although the ferromagnetism in general DMS systems originates from p-type carriers, (In,Fe)As and (In,Fe)Sb show electron-induced ferromagnetism. However, the microscopic mechanisms of such high Curie temperature and electron-induced ferromagnetism are still not clear. To understand the origin of such novel magnetic properties, we investigate the electronic structure, magnetic properties, and structural stabilities in the Fe-doped III-V semiconductors by the Korringa-Kohn-Rostoker (KKR) Green's function method within the density functional theory. It is found, from our calculations, that the intrinsic Fe-doped III-V semiconductors have strong antiferromagnetic interaction due to the super-exchange mechanism. By both n- and p-type dopings, i.e. changing the Fermi energy, we can drastically change the magnetic states from the antiferromagnetic to ferromagnetic ordering. This magnetic transition can be well understood by the Alexander-Anderson-Moriya mechanism. On the basis of our calculations, we also propose a new method for the control of magnetization by electric field (gate voltage). |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K21.00007: The origin of ferromagnetism in transition-metal doped Ge by the first principles calculations Hikari Shinya, Tetsuya Fukushima, Akira Masago, Kazunori Sato, Hiroshi Katayama-Yoshida Recently, Ge-based DMSs have attracted much attention due to many advantages for practical applications and consistencies with the general Si-SMOS technology. However, there has been great discussion about ferromagnetic mechanisms in Fe- and Mn-doped Ge-based DMSs. In this work, we investigate the electronic structures, structural stabilities, magnetic exchange coupling constants, and Curie temperature, and clarify origins of the ferromagnetism, by the density functional theory calculations. In both the (Ge,Fe) and (Ge,Mn) cases, the inhomogeneous distribution of the magnetic impurities plays an important role to determine the magnetic states. By the spinodal nano-decomposition, the Fe impurities in Ge gather together with keeping the diamond structure, so that the number of the first-nearest-neighbor Fe pairs with strong ferromagnetic interaction increases. Therefore, the Curie temperature drastically increases with the progress of the annealing. On the other hand, in (Ge,Mn) case, the other ferromagnetic ordered phases with different crystal structures tend to occur and might be an origin of high Curie temperature. |
Wednesday, March 7, 2018 9:48AM - 10:00AM |
K21.00008: Stepping stone mechanism: carrier-free long range magnetism mediated by magnetized cation states Chunkai Chan, Xiaodong Zhang, Yiou Zhang, Kin Fai Tse, Bei Deng, Jingzhao Zhang, Junyi Zhu The long range magnetism observed in group-V tellurides is the only working example of carrier-free dilute magnetic semiconductors (DMS), but the physical mechanism is unclear. Based on DFT calculations, we discovered a new ferromagnetic order in Cr-doped Bi2Te3 and Sb2Te3, with the dopant separation more than 9 Å. This configuration is the global energy minimum among all configurations. Different from the conventional super exchange theory, the magnetism is facilitated by the lone pair derived anti-bonding states near the cations. Such anti-bonding states work as stepping stones merged in the electron sea and conduct magnetism. Further, spin orbit coupling induced band inversion was found insignificant in the magnetism. Our findings directly dismiss the common misbelief that band topology is the only factor that enhances the magnetism. We further demonstrated that removal of the lone pair derived states destroys the long range magnetism. This novel mechanism sheds light on the fundamental understanding of long range magnetism and may lead to discoveries of new classes of DMS. |
Wednesday, March 7, 2018 10:00AM - 10:12AM |
K21.00009: Magnetism of Magnetic Impurity Doped GaN Modulated by Spinodal Decomposition Akira Masago, Hikari Shinya, Tetsuya Fukushima, Kazunori Sato, Hiroshi Katayama-Yoshida GaN is expected as a material of full-color monolithic light emitting diodes (LEDs), because GaN and InGaN are known as materials of blue and green LEDs, respectively and Eu-doped GaN enabled to fabricate red LEDs. Eu-doped GaN possesses not only an ability to emit light but also magnetic properties and self-generated modulations by spinodal decomposition. This property provides us with an expectation of fabrication of multifunctional materials for spintronics. We investigate magnetism of magnetic Eu-doped GaN modulated by spinodal decomposition using the density functional calculations and the Monte-Carlo simulations. As a result, we obtain that the larger cluster of EuN causes hystereses of magnetization as a function of external magnetic field. In this talk, we will discuss the magnetism, the critical temperatures, and an effect of the magneto-crystalline anisotropies. |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K21.00010: Single Crystal Growth and Propertis Study of Diluted Magnetic Semicondutor (Ba,K)(Zn,Mn)2As2 & (Ba,Na)(Zn,Mn)2As2 Guoqiang ZHAO
|
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K21.00011: Interplay of carrier free and carrier mediated magnetism in Mn doped LiZnAs Xiaodong Zhang, Jingzhao Zhang, Junyi Zhu The interplay of superexchange and Zener/RKKY and its influence on dopant distribution is studied by model systems of Mn doped LiZnAs based on density functional theory (DFT) calculations. We found that in carrier free configurations, it favors short range magnetic interaction. However, when hole is introduced, the interplay mechanism between the super exchange and the band coupling mechanism dramatically changes the magnetic coupling distance and the type of magnetic coupling. As a result, the short range ferromagnetism almost vanishes while the long range ferromagnetism remains strong. This discovery contradicts the “common sense” that magnetic interaction is strongest in the short range and decay with distance. Such interplay may be promising in designing strategies that promote stable long range magnetic configuration in experiments, which is the key to realize dilute magnetic semiconductor devices. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K21.00012: Spin driven emergent antiferromagnetism and metal insulator transition in nanoscale p-Si Paul Lou, Sandeep Kumar The entanglement of the charge, spin and orbital degrees of freedom can give rise to emergent behavior especially in thin films, surfaces and interfaces. Often, materials that exhibit those properties require large spin orbit coupling. We hypothesize that the emergent behavior can also occur due to spin, electron and phonon interactions in widely studied simple materials such as Si. That is, large intrinsic spin-orbit coupling is not an essential requirement for emergent behavior. The central hypothesis is that when one of the specimen dimensions is of the same order (or smaller) as the spin diffusion length, then non-equilibrium spin accumulation due to spin injection or spin-Hall effect (SHE) will lead to emergent phase transformations in the non-ferromagnetic semiconductors. In this experimental work, we report spin mediated emergent antiferromagnetism and metal insulator transition in a Pd (1 nm)/Ni81Fe19 (25 nm)/MgO (1 nm)/p-Si (~400 nm) thin film specimen. The spin-Hall effect in p-Si, observed through spin-Hall magnetoresistance behavior, is proposed to cause the spin accumulation and resulting emergent behavior. Such phase transition is discovered from the diverging behavior in longitudinal third harmonic voltage related to the thermal conductivity and heat capacity. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700