Exchange spin waves in thin films with gradient composition

TL;DR

This paper investigates exchange spin waves in non-uniform ferromagnetic thin films, demonstrating how compositional gradients can be engineered for advanced magnonic applications.

Contribution

It introduces a method to analyze exchange spin waves in gradient composition films and provides quantitative parameters for Pd-Fe alloys, highlighting potential for high-frequency magnonic devices.

Findings

Observation of anomalous perpendicular standing spin waves

Quantification of exchange stiffness constant as 15 T·nm²

Demonstration of engineering thin films for magnonic applications

Abstract

We report investigation of ferromagnetic resonance phenomenon in ferromagnetic thin films with essentially non-uniform composition. Epitaxial Pd-Fe thin film with linear distribution of Fe content across the thickness is used as the model material. Anomalous perpendicular standing spin waves are observed and quantified using the collective dynamic equation. Numerical analysis yields the exchange stiffness constant for diluted Pd-Fe alloy $D=2A/\mu_0M_s=15$~T$\cdot$nm$^2$ and the ratio of the effective magnetization to the saturation magnetization $M_{eff}/M_s=1.16$. It is demonstrated that, overall, engineering of thin films with non-uniform composition across the thickness can be used for high-frequency or low-field magnonic operations using exchange spin waves.