An Efficient Geometric Integrator for Thermostatted Anti-/Ferromagnetic Models

(Anti)-/ferromagnetic Heisenberg spin models arise from discretization of Landau–Lifshitz models in micromagnetic modelling. In many applications it is essential to study the behavior of the system at a fixed temperature. A formulation for thermostatted spin dynamics was given by Bulgac and Kusnetsov, which incorporates a complicated nonlinear dissipation/driving term while preserving spin length. It is essential to properly model this term in simulation, and simplified schemes give poor numerical performance, e.g., requiring an excessively small timestep for stable integration. In this paper we present an efficient, structure-preserving method for thermostatted spin dynamics.     

A Different Laboratory Tale: Fifty Years of Mössbauer Spectroscopy

I explore the fifty-year development of M?ssbauer spectroscopy by focusing on three episodes in its development at Argonne National Laboratory: work by nuclear physicists using radioactive sources in the early 1960s, work by solid-state physicists using radioactive resources from the mid- 1960s through the 1970s,and work by solid-state physicists using the Advanced Photon Source from the 1980s to 2005. These episodes show how knowledge about the properties of matter was produced in a national-laboratory context and highlights the web of connections that allow nationallaboratory scientists working at a variety of scales to produce both technological and scientific innovations.     

Dynamic susceptibility of thin films with perpendicular magnetic anisotropy

We investigate the spin dynamics related to the Gilbert damping constant in infinite continuous thin films with perpendicular magnetic anisotropy (PMA), based on numerical and analytic approaches. We obtain the dynamic susceptibility of the infinite continuous thin films with various PMA energies by using micromagnetic simulations with periodic boundary conditions. These results are compared with the analytic solution that we derived from the Landau–Lifshitz–Gilbert equation. Based on our numerical and analytic studies, we support the physical analysis for results in the experimental determination of the Gilbert damping constant for PMA materials.     

Weak martingale solutions to the stochastic Landau–Lifshitz–Gilbert equation with multi-dimensional noise via a convergent finite-element scheme

We propose an unconditionally convergent linear finite element scheme for the stochastic Landau–Lifshitz–Gilbert (LLG) equation with multi-dimensional noise. By using the Doss–Sussmann technique, we first transform the stochastic LLG equation into a partial differential equation that depends on the solution of the auxiliary equation for the diffusion part. The resulting equation has solutions absolutely continuous with respect to time. We then propose a convergent $\theta$-linear scheme for the numerical solution of the reformulated equation. As a consequence, we are able to show the existence of weak martingale solutions to the stochastic LLG equation.     

Some blowup solutions about two systems derived from Landau–Lifshitz–Gilbert equation

Two different systems which can be regard as the extreme cases of Landau-Lifshitz–Gilbert equation are considered. When the gyromagnetic term of Landau–Lifshitz–Gilbert equation vanishes away, we consider some special solutions for a modified harmonic map heat flow which map from (2+1)$(2+1)$-dimensional space–time into the 2-sphere. The existence of regular initial data leading to blow up in finite time is established. When the Gilbert term is omitted, a blowup solution is obtained by constructing a blowup solution of Landau–Lifshitz equation.     

Spin pumping at the Co2FeAl0.5Si0.5/Pt interface

Spin pumping at the Co2FeAl0.5Si0.5/Pt and Pt/Co2FeAl0.5Si0.5 interfaces has been studied by ferromagnetic resonance technology(FMR). The spin mixing conductance of the Co2FeAl0.5Si0.5/Pt and Pt/Co2FeAl0.5Si0.5 interfaces was determined to be 3.7×1019m 2and 2.1×1019m 2 by comparing the Gilbert damping in a Co2FeAl0.5Si0.5single film, Co2FeAl0.5Si0.5/Pt bilayer film and a Pt/Co2FeAl0.5Si0.5/Pt trilayer film. Spin pumping is more efficient in the Co2FeAl0.5Si0.5/Pt bilayer film than in permalloy/Pt bilayer film.     

Theoretic 3-D study of the high-frequency magnetic moment dynamics in thin ferromagnetic films with in-plane uniaxial anisotropy by considering eddy-current generation

In the present paper, theoretic investigations of polarisation vector precession trajectories represented by a macro spin in ferromagnetic films with in-plane uniaxial anisotropy were realised. For this purpose, the Landau–Lifschitz–Gilbert differential equation (LLG) in combination with the Maxwell equations were solved for three dimensions by considering a linear progression of the magnetisation or polarisation with an external field. The frequency and time dependent polarisation trajectories illustrate how a magnetic moment precesses if effective damping and eddy-currents impacts its motion. For computation, typical parameter values like the saturation polarisation J_s=μ₀·M_s=1.4 T and in-plane uniaxial anisotropy μ₀·H_u=4.5 mT were employed. The main focus of simulation was on the variation of the effective damping parameter α_eff between 0.01 and 0.05 and ferromagnetic film thickness t_m between 200 nm and 1200 nm. The frequency-dependent calculations were carried out between 50 MHz and 6 GHz. The time-dependent simulations were done for a duration between 5 and 30 ns.