Measuring spin wave resonance in Ni100-xFex films: Compositional and temperature dependence

Abstract

We study the composition and temperature dependence of the spin wave resonance in Ni100-xFex films, where, x is 40% or below, with a thickness of 100 nm using a temperature variable broadband ferromagnetic resonance (FMR) spectroscopy. From the uniform FMR mode, the saturation magnetization (Ms) and the Gilbert damping (α) are measured, and using the first perpendicular standing spin wave mode, the exchange stiffness constant (A) is determined. At lower temperatures, we measure an increase of both Ms and A, while α shows a very weak temperature dependence. We find that Ms follows perfectly Bloch’s law, while A is best described by a T2 law. Additionally, we measure a linear increase in Ms and A with the increase of Fe content in films, while α strongly decreases. The compositional variation of α and A can be ascribed to the increase of Ms in Fe-rich films. Furthermore, we estimate the exchange length (Lex) in Ni100-xFex films. We find that Lex is temperature independent, however, a strong decrease of Lex is measured in Fe-rich films. This reduction is inversely proportional to √Ms © 2021 IOP Publishing Ltd.