Nonlinear and Thermal Effects in the Absorption of Microwaves by Random Magnets

TL;DR

This paper investigates how microwave absorption by random-anisotropy magnets depends on temperature and power, revealing nonlinear effects and a transition to transparency at higher temperatures due to heating and barrier crossing.

Contribution

It demonstrates the nonlinear microwave absorption behavior in random magnets caused by heating and metastability, extending previous linear regime studies.

Findings

Microwave absorption decreases dramatically at elevated temperatures.

Heating induces nonlinear spin transitions across energy barriers.

Random magnets become transparent to microwaves at high temperatures.

Abstract

Abstract We study the temperature dependence of the absorption of microwaves by random-anisotropy magnets. It is governed by strong metastability due to the broad distribution of energy barriers separating different spin configurations. At a low microwave power, when the heating is negligible, the spin dynamics is close to linear. It corresponds to the precession of ferromagnetically ordered regions that are in resonance with the microwave field. Previously we have shown (doi.org/10.1103/PhysRevB.103.214414) that in this regime a dielectric substance packed with random magnets would be a strong microwave absorber in a broad frequency range. Here we demonstrate that on increasing the power, heating and over barrier spin transitions come into play, resulting in the nonlinear behavior. At elevated temperatures the absorption of microwave power decreases dramatically, making the dielectric substance with random magnets transparent for the microwaves.