Bulletin of the American Physical Society
2017 Annual Meeting of the APS Mid-Atlantic Section
Volume 62, Number 19
Friday–Sunday, November 3–5, 2017; Newark, New Jersey
Session H2: CMP-QM: Magnetic Solitons / NSF |
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Chair: Oleg Tchernyshov, Johns Hopkins University Room: Ballroom B, Campus Center, NJIT |
Saturday, November 4, 2017 2:00PM - 2:36PM |
H2.00001: Mechanics of magnetic solitons Invited Speaker: Oleg Tchernyshyov Magnets host a variety of solitons that are stable for topological reasons: domain walls, vortices, and skyrmions, to name a few. Because of their stability, topological solitons can potentially be used for storing and processing information. This motivates us to build economic, yet realistic models of soliton dynamics in magnets. E.g., a domain wall in a cylindrical ferromagnetic wire can be pictured as a bead on a string, which can move along the string and rotate about its axis. Its mechanics is counterintuitive: it rotates when pushed and moves when twisted. Attempts to define the linear momentum of a topological soliton often yield paradoxical results. I will review basic models of ferro- and antiferromagnetic domain walls in one dimension and give examples from higher dimensions. [Preview Abstract] |
Saturday, November 4, 2017 2:36PM - 2:48PM |
H2.00002: Nonreciprocal dynamics of domain wall in a finite ferromagnetic thin film Shu Zhang, Oleg Tchernyshyov We give a minimum model for the dynamics of a domain wall in a ferromagnetic thin film with the easy axis perpendicular to the film plane. The domain wall is modeled as a string whose Lagrangian, in addition to the standard string tension and kinetic energy, possesses a Berry phase term reflecting the precessional dynamics of spins. We solve analytically the equations of motion of such a string on which waves propagating left and right have different speeds. The string with free boundary conditions translates uniformly with a speed set by the initial configuration. The dynamics driven by an in-plane and an out-of-plane magnetic field is also derived. A sudden application of an in-plane field on a flat string results in the appearance of kinks (slope discontinuities) on the string, which propagate back and forth along it. [Preview Abstract] |
Saturday, November 4, 2017 2:48PM - 3:00PM |
H2.00003: Dynamics of antiferromagnetic solitons Sayak Dasgupta, Oleg Tchernyshyov We study the dynamics of topological solitons in antiferromagnets using a Lagrangian formalism constructed in terms of collective coordinates representing the soft modes of the defect. We adopt a procedure by which we can effectively study the interplay of internal exchange fields and external fields (magnetic and spin current) which allows us to determine whether solitons can be moved and under what conditions. In our investigation we consider the examples of one dimensional domain walls and planar vortices focusing on their dynamics. It turns out that to effectively move the soliton either a finite ferromagnetic moment has to be induced through an asymmetric exchange, or there must be internal forces exerting a static friction on the defect. We also outline a procedure, using a crossed magnetic (out of plane) and spin current field, by which one can move antiferromagnet vortices in planar geometries without the requirement of an asymmetric exchange. [Preview Abstract] |
Saturday, November 4, 2017 3:00PM - 3:12PM |
H2.00004: The Annihilation of Vortex Anti-Vortex Pairs Derek Reitz, Oleg Tchernyshyov We study theoretically the annihilation of a vortex-antivortex pair in a two-dimensional easy-plane ferromagnet. For opposite out-of-plane orientations of the vortex cores, the two solitons orbit each other. In the presence of finite damping, the radius of the orbit gradually decreases until the cores overlap. We compare predictions of analytical theory to results of micromagnetic simulations. [Preview Abstract] |
Saturday, November 4, 2017 3:12PM - 3:48PM |
H2.00005: Update on CMP and Quantum Materials at NSF Invited Speaker: Tomasz Durakiewicz The Condensed Matter Physics program at the Division of Materials Research, NSF, supports experimental, as well as combined experiment and theory projects investigating the fundamental physics behind phenomena exhibited by condensed matter systems. Representative research areas in such systems include: 1) phenomena at the nano- to -macro-scale including: transport, magnetic, and optical phenomena; classical and quantum phase transitions; localization; electronic, magnetic, and lattice structure or excitations; superconductivity; and nonlinear dynamics. 2) low-temperature physics: quantum fluids and solids; 1D {\&} 2D electron systems. 3) soft condensed matter: partially ordered fluids, granular and colloid physics, and 4) understanding the fundamental physics of new states of matter as well as the physical behavior of condensed matter under extreme conditions e.g., low temperatures, high pressures, and high magnetic fields. In this presentation I will describe the current status of CMP program and discuss some of the program development activities and opportunities related to the NSF's Quantum Leap Big Idea, especially in the area of Quantum Materials. [Preview Abstract] |
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