Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session L3: Magnetism |
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Chair: Puru Jea, Virginia Commonwealth University Room: Monroe Room |
Saturday, November 12, 2016 8:30AM - 9:06AM |
L3.00001: High Field Magneto-Optical Studies of Ferromagnetic InMnSb and InMnAs: Spin-Orbit-Split Hole Bands and g-Factors Invited Speaker: Giti Khodaparast Carrier-induced ferromagnetism in magnetic III-V semiconductors has opened up several opportunities for device applications as well as for fundamental studies of a material system in which itinerant carriers interact with the localized spins of magnetic impurities. The origin of the carrier-induced ferromagnetism is still an open and exciting question. In order to begin to understand the hole mediated ferromagnetism, probing the band structure in these material systems is crucial. Here we present Cyclotron Resonance (CR) and Magnetic Circular Dichroism (MCD) studies on InMnSb and InMnAs films. The measurements were performed on samples with different Mn contents and external magnetic fields ranging up to 120 Tesla for the CR, and 31 Tesla for the MCD measurements. We compared Landau level and band structure calculations with our experimental measurements. [1-4]. \newline [1] G. A. Khodaparast,Y. H. Matsuda, D. Saha, G. D. Sanders, C. J. Stanton, H. Saito, S. Takeyama, T. R. Merritt, C. Feeser, B. W. Wessels, X. Liu and J. Furdyna, Phys. Rev. B, 88, 235204 (2013). [2] M. Bhowmick, T. R. Merritt, and G. A. Khodaparast, Bruce W. Wessels Stephen A. McGill, D. Saha, X. Pan, G. D. Sanders, and C. J. Stanton, Phys. Rev. B, 85, 125313 (2012). [3] Y Sun, FV Kyrychenko, GD Sanders, CJ Stanton, GA Khodaparast, J Kono, YH Matsuda, H Munekata “Probe of the Band Structure of MBE Grown p-Type InMnAs at Ultrahigh Magnetic Fields”, SPIN Vol. 5, No. 1,1550002 (2015). [4] M. A. Meeker, B. A. Magill, G. A. Khodaparast, D. Saha, C. J. Stanton, S. McGill, and B. W. Wessels “High-field magnetic circular dichroism in ferromagnetic InMnSb and InMnAs: Spin-orbit-split hole bands and g factors”, Phys. Rev. B 92, 125203 (2015). \newline Collaborators: Brenden Magill and Michael Meeker: Virginia Tech, Christopher J. Stanton and Dipta Saha: Univ. of Florida, Bruce Wessels, Northwestern Univ., Jacek Furdyna and Xinyu Li: Univ. of Notre Dame, Yasuhiro Matsuda, Univ. of Tokyo (Kashiwa), Steve McGill, NHMFL. [Preview Abstract] |
Saturday, November 12, 2016 9:06AM - 9:42AM |
L3.00002: Amorphous Magnetic Films Invited Speaker: Joseph Poon Recently, amorphous rare-earth-transition-metal ($a$-RE-TM) thin films with perpendicular magnetic anisotropy (PMA) are being studied for spin-based nanoelectronics. These amorphous ferromagnetic films exhibit strong PMA, coercivity field of several Tesla and anisotropy energy \textasciitilde 10$^{\mathrm{6\thinspace }}$erg/cm. $a$-RE-TM is a ferrimagnet containing antiferromagnetically coupled ferromagnetic RE and TM sublattices. The sublattices magnetization compensates each other at the compensation temperature (T$_{\mathrm{comp}})$. Due to the unusual atomic scale structure and wide compositional range of these amorphous films, novel magnetic states can be obtained by appropriately configuring the nanoscale structure. The mechanisms are verified by micromagnetic and atomistic simulations, to be presented in two oral presentations. The ability to control these new properties in amorphous films without the need for epitaxial growth opens a new avenue for enhancing the functionalities of spin-based materials. [Preview Abstract] |
Saturday, November 12, 2016 9:42AM - 10:18AM |
L3.00003: Magnetism in Nanosystems Invited Speaker: Jian Zhou Magnetism is an old physics topic that has been receiving new concept in recent years. One of the reason is the discussion of magnetism in nanostructured systems, especially in two-dimensional (2D) thin films. Among different types of magnetic couplings, ferromagnetism is the simplest but most useful one. In the present talk, I will discuss some ferromagnetic thin films with their novel and interesting properties. Using first-principles calculations we have discovered and demonstrated a series of transition metal (TM) liganded ferromagnetic tri-layer thin films, including FeC$_{\mathrm{2}}$, MnO$_{\mathrm{2}}$, and RuI$_{\mathrm{3}}$. The 2D FeC$_{\mathrm{2}}$ can be chemically exfoliated from bulk ThFeC$_{\mathrm{2}}$ compound, which has a Curie temperature of \textasciitilde 245 K, and shows a 100{\%} spin polarization at the Fermi level. The MnO$_{\mathrm{2}}$ layer has a strain modulated Curie temperature in the range of 140--220 K, and shows a semiconducting conductivity. Furthermore, we show that the MnO$_{\mathrm{2}}$ is a good substrate to support a single layer of Sb/Bi. The combined system possesses a large band gap of quantum spin Hall effect (without time-reversal symmetry) and a large anomalous Hall effect, in their low energy state. In order to achieve intrinsic and robust quantum anomalous Hall effect in experimentally feasible 2D materials, we propose that TM halide family is a good candidate. Using ferromagnetic RuI$_{\mathrm{3}}$ thin film as an example, we show that its Curie temperature is \textasciitilde 360 K. At the Fermi level it shows a clear Dirac cone in the spin down channel, which can be opened once the spin rotational symmetry is broken by including spin-orbit coupling. We demonstrate a large band gap of quantum anomalous Hall effect emerges inside the band gap, and the metallic edge band can be clearly seen in a nanoribbon model. These findings broaden the potential applications of low-dimensional magnetic materials. [Preview Abstract] |
Saturday, November 12, 2016 10:18AM - 10:54AM |
L3.00004: From materials to circuits: Multiscale modeling of nano-magnetic switches Invited Speaker: Avik Ghosh Over the last decade, a rich variety of magnetic switching phenomena have appeared on the horizon, including spin torque, straintronics, Giant Spin Hall, voltage controlled magnetic anisotropy. These studies have led to the design and exploration of nanomagnetic devices such as MRAMs, STTRAMs, STNOs, CSL, ASL, stochastic, neuromorphic and so on. Each device must occupy a complex multi-dimensional phase space defined by an energy budget, a desired speed and a target read-write-retention error rate. To identify fundamental limitations and design better magnetic switches, we have developed a multiscale simulation tool that goes from material to circuit level performance metrics, and identifies key challenges along the way. At the lowest level, we start with Density Functional Theory (DFT) to identify magnetic alloys from the Heusler family that form stable half-metals. Heterojunctions and superlattices made out of these materials are predicted to give us high magnetic anisotropy and high polarization. We can then incorporate the DFT complex bands, or their simplified continuum versions, into a quantum kinetic transport solver based on the Non-Equilibrium Green’s Function (NEGF) formalism to extract the tunnel magnetoresistance, spin current and spin torque. At this stage, we can add phenomenological spin-flip scattering (e.g. from magnons) as additional self-energy matrices. Finally, the current is incorporated into a micromagnetic solver that computes the results for a stochastic Landau-Lifschitz-Gilbert (LLG) equation to evaluate the switching dynamics. Instead of a Monte-Carlo sampling of the noise, we can directly evaluate the switching probability distribution using a fast Fokker-Planck approach that calibrates well with empirical models over the entire parameter range (sub-critical to super-critical switching). We discuss various ways to carry through these steps, and the challenges and opportunities we see with magnetic switching based on our simulations. [Ref: Spin Transfer Torque: A Multiscale Picture”, Yunkun Xie, Ivan Rungger, Kamaram Munira, Maria Stamenova, Stefano Sanvito and Avik W. Ghosh, Nanomagnetic and Spintronic Devices for Energy-Efficient Memory and Computing, (eds J. Atulasimha and S. Bandyopadhyay), John Wiley & Sons, Ltd, Chichester, UK (2016).] [Preview Abstract] |
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