Domain Wall Collision-Induced Spin Waves

Tristain Delaney

doi:10.21061/jumr.v5i0.1503

Abstract

A series of micromagnetic simulations are conducted whereby two transverse domain walls are injected into a straight magnetic nanowire under an applied field. It is found that, based on the relative orientation of the domain walls, the two may annihilate, resulting in the generation of an intense spin-wave burst. Since the applied magnetic fields for these simulations are smaller than the Walker breakdown field, these results present an extremely low-energy means of generating and controlling spin waves for engineering applications.

Highlights

1.1 Spin Wave FundamentalsThe temporal evolution of the magnetization vector M(r) in a material is given by the Landau-Lifschitz-Gilbert (LLG) Equation, where α is the phenomenological damping constant, γ is the gyromagnetic ratio, m is the unit magnetization vector, and H is the effective field comprised of the exchange, dipolar, anisotropic, and external applied fields acting upon M
The dispersion relations were determined by calculating the Discrete Fourier Transform of the z-component magnetization for a 400 nm line of cells within the middle of the nanowire for 2 nanoseconds after the external Oersted field was applied, and are plotted on a logarithmic scale since the Fast Fourier Transform (FFT) power of all possible modes scales several orders of magnitude
This paper presents an efficient and generally simple means of generating Spin waves (SWs) by controlling the orientation of two transverse wall (TW) so that they will annihilate upon contact

Summary

Introduction

1.1 Spin Wave FundamentalsThe temporal evolution of the magnetization vector M(r) in a material is given by the Landau-Lifschitz-Gilbert (LLG) Equation, where α is the phenomenological damping constant, γ is the gyromagnetic ratio, m is the unit magnetization vector, and H is the effective field comprised of the exchange, dipolar, anisotropic, and external applied fields acting upon M. SWs were first observed as resonant microwave modes of the magnetization in ferrite samples[1] The nature of these modes was later derived analytically by Walker[2] for spheroids and Damon and Eschbach[3] for ferromagnetic slabs, in the long-wavelength limit of strictly dipolar modes by simultaneously solving Equation 1 together with Maxwell’s Equations. In both works, only dipole-dipole interactions are taken into account as this allows one to analytically derive the nature of the resonant modes; the modes have a long-wavelength, low frequency character which makes them only applicable on the scale of several millimeters. Many of the applications for these resonant modes in ferrite have been in the areas of measurement and material characterization,[11] antennae,[12] and other applications where a characteristic length of more than a few micrometers is desired

Methods

Results

Conclusion