Event
PhD Dissertation Defense: Ziyu Liu
Tuesday, November 12, 2013
10:00 a.m.
Room 2328, AVW Bldg.
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: PhD Dissertation Defense
Name: Ziyu Liu
Date/Time: Tuesday, November 12th, 2013 at 10:00AM
Location: Room 2328, AVW Building
Committee:
Prof. Isaak Mayergoyz, Advisor/Chair
Prof. Julius Goldhar
Prof. Edo Waks
Prof. Sennur Ulukus
Prof. Howard Elman, Dean's Representative
Title: Modeling of Random Magnetization Dynamics in Nanosystems
Abstract:
Understanding magnetization dynamics in nano-scale magnetic systems is of great scientific interests for its application to magnetic recording technology and spintronic devices. Recently, a novel approach to modeling stochastic magnetization dynamics has been proposed. In this approach, thermal bath effects are accounted for by introducing a jump-noise torque term in the precessional magnetization dynamics equation. In this dissertation, we develop a Monte Carlo type numerical technique for implementation of the approach. There are two central elements of our numerical technique: a ``midpoint'' finite-difference scheme for integration of deterministic precessions and a ``self-scattering'' scheme which results in time-homogenization of a jump-noise process. We also perform and illustrate numerous Monte Carlo simulations in the dissertation using numerical examples. The Monte Carlo simulations are ideally suited for implementation on GPUs since they are intrinsically parallelizable in the sense that different realizations of stochastic magnetization dynamics can be computed concurrently. Therefore we develop a parallel algorithm and implement it using a Nvidia GPU. A speed-up factor of about 200 is achieved using this GPU implementation in comparison with the tranditional CPU single threaded implementation. Furthermore, we apply the jump-noise process driven Landau-Lifshitz equation to the study of thermal magnetization switching for a very wide range of temperatures. Numerical calculations demonstrate that the magnetization switching rate has a different temperature dependence at relatively high and very low temperatures. The high temperature switching conforms to the Arrhenius law of thermal activation, whereas the low temperature switching has many features traditionally attributed to the phenomenon of macroscopic magnetization tunneling. Finally, we extend the jump-noise process approach to the study of magnetization dynamics at elevated temperatures. We derive a generalization of the classical Landau-Lifshitz equation to describe magnetization dynamics around Curie temperature where the traditional micromagnetic constraint is not valid.
