Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E38: Theoretical Underpinnings of MagnetismFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Felix Buettner, Massachusetts Institute of Technology Room: BCEC 206B |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E38.00001: Mapping of a thin-film ferromagnet to electrodynamics Oleg Tchernyshyov, Sayak Dasgupta, Shu Zhang, Michael Bjerngaard We consider a field-theoretic description of a thin-film ferromagnet with easy-plane anisotropy. An extension of the well-known duality with electrostatics in 2-dimensional space to (2+1)-dimensional spacetime maps this system to a theory of electrodynamics. The low-energy description is the familiar Maxwell electrodynamics. Spin waves become electromagnetic waves, whereas vortices turn into particles whose electric charge equals the vortex number. Vortices have no inertia but experience a Lorentz-like force due to a background magnetic field whose strength is equal to spin density. This mapping allows us to calculate the emission of spin waves by rotating vortices using the direct analogy with the emission of electromagnetic waves by a rotating electric dipole. |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E38.00002: Mapping of a thin-film ferromagnet to electrodynamics: quantum statistics of vortices Shu Zhang, Sayak Dasgupta, Michael Bjerngaard, Oleg Tchernyshyov We consider a field-theoretic description of a thin-film ferromagnet with easy-plane anisotropy. The system can be mapped to the electrodynamics theory in (2+1)-dimensional space-time. The low-energy description is the familiar Maxwell electrodynamics. Spin waves become electromagnetic waves, whereas vortices turn into particles whose electric charge equals the vortex number n. A careful analysis of the high-energy theory reveals that these particles also carry a magnetic flux equal to the net spin of the vortex core Sz. Braiding two identical vortices yields an Aharonov-Bohm phase exp(2π i n Sz), which may lead to a nontrivial quantum statistics of vortices. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E38.00003: Mapping of a thin-film ferromagnet to electrodynamics: emission of spin waves by vortices Michael Bjerngaard, Sayak Dasgupta, Shu Zhang, Oleg Tchernyshyov We consider a field-theoretic description of a thin-film ferromagnet with easy-plane anisotropy. An extension of the well-known duality with electrostatics in 2-dimensional space to (2+1)-dimensional spacetime maps this system to a theory of electrodynamics. The low-energy description is the familiar Maxwell electrodynamics. Spin waves become electromagnetic waves, whereas vortices turn into particles whose electric charge equals the vortex number. This analogy allows us to compute the emission of spin waves by a rotating vortex-antivortex pair. Energy dissipation from this process becomes noticeable when the pair separation decreases below a characteristic length scale of order $\alpha^{-1/2}R$, where $R$ is the radius of the vortex core and $\alpha$ is the Gilbert constant. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E38.00004: Calculation of nonlinear susceptibility in magnetic systems Yuriy Sizyuk, Peter P. Orth Coherent nonlinear optical spectroscopy has been a successful tool to probe interactions between excitations in NMR and semiconductor experiments. Recent advances of optical experiments in the terahertz range allows the realization of similar measurements for localized magnetic systems. Anticipating this, we are calculating nonlinear magnetic susceptibilities for well known models, such as the transverse field Ising model, and Kitaev honeycomb model. The information about the magnetic excitations can then be used as a probe to experimentally identify complex, yet elusive magnetic ground states, such as quantum spin liquids. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E38.00005: Energy-momentum tensor of a ferromagnet Sayak Dasgupta, Oleg Tchernyshyov The energy-momentum tensor provides valuable information about a physical system. Deriving this quantity for a ferromagnet runs into a conceptual difficulty associated with the presence of gyroscopic forces, which are represented by spin Berry-phase terms in the Lagrangian. Their gauge dependence and lack of rotational symmetry lead to paradoxes. E.g., the adiabatic spin torque exerted on a domain wall by a spin-polarized current is either missing or contains unphysical glitches, depending on the gauge choice. It is therefore desirable to derive a gauge-invariant and rotationally symmetric version of the energy-momentum tensor. We achieve this by using the gauge-invariant and symmetric Wess-Zumino action for spins at the expense of introducing an extra dimension, with the ferromagnet living on its boundary. The energy-momentum tensor defined in this (d+2)-dimensional spacetime yields correct physical answers. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E38.00006: A measurable form of Bell's correlation of spin currents across a double dot in the Kondo regime Rui Sakano, Akira Oguri, Yunori Nishikawa, Eisuke Abe We investigate Bell-state correlations of quasiparticle pairs that are excited within nonlinear current through a double dot in the Kondo regime. Using the renormalized perturbation expansion in the residual interaction of the local Fermi liquid, we calculate an asymptotically exact form of Bell's correlation at low energies. We find that the exchange interaction of the double dot violates Bell's inequality. We especially suggest a measurable form of Bell's inequality that is given by correlations of the full current across the double dot. We illustrate the exchange interaction dependence of upper limits of the suggested Bell's correlation in the quantum theory and the hidden variable theory, using the numerical renormalization group calculation. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E38.00007: Evolution of magnetic Dirac bosons in a Kagome lattice Daniel Boyko, Alexander Balatsky, Avadh Saxena, Jason Haraldsen We examine the magnetic properties and spin dynamics of Dirac nodes in a Heisenberg kagome lattice. Using linear spin theory, the phase diagrams and the evolution of exchange interactions in various magnetic configurations of the Kagome lattice are numerically calculated and produce spin waves that contain bosonic Dirac and Weyl points. Through the frustration of the magnetic geometry, we see a connection to the symmetry properties of the kagome lattice and the various antiferromagnetic configurations, where further study of external frustrations from a magnetic field, temperature, and anisotropy may reveal a controllability of the exchange interactions and nodal points. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E38.00008: How many tunable parameters to attain a spin degeneracy between Landau levels? Chong Wang, Duan Wenhui, Leonid Glazman, Aris Alexandradinata The spin degeneracy of Landau levels is generically lifted by the Zeeman interaction, and also by the spin-orbit coupling in non-centrosymmetric solids. In the absence of any crystalline point-group symmetry, such a spin degeneracy can only be found by tuning three real parameters; we have exhaustively identified all symmetry classes of solids for which this number is reduced from three. In particular, only one parameter is needed in the presence of rotational symmetry; this parameter may be the magnitude or orientation of the field, or the bias voltage in tunneling spectroscopy. Signatures of single-parameter tunability include: (i) a smooth crossover between period-doubled and -undoubled quantum oscillations in the low-temperature Schubnikov-de Haas effect, and (ii) "magic angle" magnetoresistance oscillations. Case study is discussed for the Rashba-Dresselhaus two-dimensional electron gas subject to an arbitrarily oriented magnetic field. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E38.00009: Implementation and application of a real-space pseudopotential method for calculating magnetocrystalline anisotropy Masahiro Sakurai, James Chelikowsky We present a real-space pseudopotential method for calculating magnetocrystalline anisotropy within relativistic density-functional theory. Our formalism is implemented in our real-space pseudopotential code, PARSEC, which is explicitly designed for an efficient implementation on a parallel computing platform (Phys. Rev. Materials 2, 084411 (2018)). We demonstrate that our formalism works well for prototypical transition-metal compounds, such as YCo5 and Mn2Ga, yielding an accurate magnetization and a magnetocrystalline anisotropy constant consistent with previous work. We also use our method to explore possible candidate materials for rare-earth-free permanent magnets. We find that ZrCo5 compounds can provide moderate magnetocrystalline anisotropy and sufficient work is supported by the National Science Foundation (NSF), DMREF-1729202. HPC resources were provided by the Texas Advanced Computing Center (TACC).saturation magnetization (Phys. Rev. Materials 2, 084410 (2018)). |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E38.00010: Strain control of the Néel vector in L10-type Mn-based antiferromagnetic materials: a first principles study In Jun Park, Roger Lake Mn-based antiferromagnetically ordered L10-type crystals such as MnIr, MnRh, MnNi, MnPd, and MnPt are of interest for possible electronic or spintronic applications. We used first-principles calculations to study the effect of strain on the magnetic anisotropy of those materials. The strain is applied along one axis (a) of the basal plane, and the structure and lattice vectors in the other two directions (b,c) are fully relaxed. We found that by applying strain, the direction of the Néel vector can be rotated by 90° for all materials. For MnIr, MnRh, MnNi, and MnPd, the Néel vector rotates within the basal plane. The sign of the effect, whether compression along the a-axis leads to a parallel or perpendicular Néel vector, depends on the specific material. MnPt is unique among this material family, since, at zero strain, its Néel vector lies along the c-axis, and strain along the a-axis rotates it into the basal plane. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E38.00011: First-principles calculations of magneto-optical Kerr effect in high Neel temperature antiferromagnetic Metals Krithik Puthalath, Kisung Kang, Andre Schleife Recent developments in spintronics have suggested the use of high Neel temperature antiferromagnetic (AFM) materials in memory devices due to their vanishing stray fields and robust magnetic structure for ultra-fast spin dynamics in the terahertz regime. In particular, the optical response of these magnetic materials via the Kerr effect (MOKE) provides an excellent method to probe surface magnetization and elucidate the AFM state under external magnetic fields. In this work, we use first-principles density functional theory calculations to obtain the fully relativistic dielectric tensor to predict MOKE signals for Cr2As, Mn2As, Fe2As, MnPt and Mn2Au under external magnetic fields. We further corroborate experimental measurements by obtaining the magnetic susceptibility from first principles using a spin-tilting method. Finally, we explore the implications of applying external magnetic bias in AFMs by interpreting the electronic band structure and its evolution with respect to spin-orbit coupling and magnetization, to better understand the origins of the predicted MOKE signals. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E38.00012: Geometrical indicators for magnetism in Pt clusters Roberto D'Agosta, Cono Di Paola, Francesca Baletto With "There is plenty of room at the bottom", Feynman points at the nanoscale where new phenomena take place, in particular when the behaviour of "a few" influences "many" particles. In particular, in nanoparticle physics, the lack of periodicity stabilises isomers whose morphology is impossible in crystalline bulk. At the same time, the physical properties of a mono-metallic nanocluster depend strongly on its shape and size. For example, catalytic properties rely on the presence of specific and diverse adsorption sites. By playing with size and shape of the nanocluster, we modify its properties towards tailored applications. We show that magnetism arising in nano-sized Pt objects is due to an effect present in the second coordination shell [1]. We demonstrate how magnetism is affected by the surrounding environment in the case of small Pt-nanoclusters embedded in zeolite pores [2]. Hopefully, we can identify geometrical indicators that help in designing clusters. |
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