Absorption of Microwaves by Random-Anisotropy Magnets

TL;DR

This paper develops a microscopic model to understand microwave absorption in random-anisotropy magnets, revealing broad frequency absorption due to domain size distribution and potential for enhanced absorption in low-dimensional materials.

Contribution

The study introduces a detailed microscopic model linking spin interactions with microwave absorption, highlighting the role of domain distribution and anisotropy in the process.

Findings

Microwave absorption occurs over a broad frequency range.

Absorption peaks depend on the ratio of anisotropy to exchange strength.

Low-dimensional systems show significantly increased absorption.

Abstract

Microscopic model of the interaction of spins with a microwave field in a random-anisotropy magnet has been developed. Numerical results show that microwave absorption occurs in a broad range of frequencies due to the distribution of Imry-Ma domains on sizes and effective anisotropy. That distribution is also responsible for the weak dependence of the absorption on the damping. At a fixed frequency of the ac-field the spatial pattern of the amplitude of spin oscillations exhibits maxima corresponding to the oscillations of resonant magnetic domains. The dependence of the peak absorption frequency on the ratio of the magnitude of per-spin random anisotropy to the strength of the ferromagnetic exchange agrees with the scaling derived from the Imry-Ma argument. The effect noticeably increases in low-dimensional systems, suggesting that materials comprised of microscopic amorphous leaves and wires can be promising candidates for enhanced microwave absorption.