Photothermally modulated magnetic resonance using a light access microwaves cavity: Influence of skin depth and of photo-injected carriers

摘要

This study reports on the modulation frequency dependence of the photothermally modulated magnetic resonance signal of a set of magnetic samples in the form of foils, layers, and thin films: 50 mu m Fe and Ni foils; 5 mu m magnetic layer of gamma-Fe2O3 in a cassette tape; and 150 nm Co and Permalloy films deposited on glass and Si (111) substrates, besides the naked Si substrate. It is shown, both by analytical calculation and by measurements, that the skin depth of the microwaves deeply influences the signal behavior by selecting the portion of the sample that is probed. Clear differences in the frequency dependence are observed between the metallic Ni and Fe foils and the dielectric gamma-Fe2O3 cassette tape. Furthermore, the thermal mismatch between the magnetic films (Co and Permalloy) and substrates (glass and Si) also plays a crucial role, once the modulation of the temperature is strongly dependent on the substrate thermal parameters at low modulation frequencies. The non-resonant signal from the diamagnetic Si is also analyzed. It is produced by the absorption of microwaves by the photo-injected free carriers and presents characteristic behavior in the investigated frequency range. Published by AIP Publishing.