Applications of the gyrocoupling vector and dissipation dyadic in the dynamics of magnetic domains

Abstract

This paper extends the theory of magnetic domains with emphasis on recent developments in ``hard bubbles''. A spin configuration of a planar Bloch wall containing periodic Bloch lines is presented which minimizes the magnetostatic energy to first order in the parameter ${\text{2πM}}_s^2{\mathrm{/K}}_u$ for arbitrary period. The form of this solution is found to suggest the form of the dynamic breakdown of this spin configuration. The remainder of the paper consists of applications of the gyrocoupling force and vector, f<sup>g</sup> = g × v and g = − (M<sub>s</sub>/|γ|)sinθ(▿θ) × (▿φ), respectively, and the dissipation force and dyadic, f<sup>a</sup> = d · v and d = − α(M<sub>s</sub>/|γ|)[(▿θ)(▿θ) + sin<sup>2</sup>θ(▿φ)(▿φ)]. The use of f<sup>g</sup> and f<sup>a</sup> produces results with fewer assumptions and with less calculation than with previous methods. The magnitude of g is found to be an invariant local measure of the ``hardness'' of the domains. Integrating f^g and f^α produces a general planar wall response function from which the hard bubble dynamic equation is obtained. It is found that the difference between the hard bubble and normal bubble damping parameters can be accounted for by examination of the hard bubble spin‐wave spectrum. An estimate of the velocity required for the production of horizontal Bloch lines is made using f^g. This velocity is a substantial fraction of the Walker velocity. The vector g is used as an aid in the visualization of the mechanism by which ion implantation suppresses hard bubbles. From the point of view of both mobility and hard bubble suppression, materials having a large in‐plane anisotropy are found to be desirable.