Spin waves in alloys at finite temperatures: application for FeCo magnonic crystal

TL;DR

This paper provides a theoretical analysis of how temperature and disorder affect spin wave spectra in FeCo magnonic crystals, highlighting their stability and damping properties relevant for spintronic applications.

Contribution

It introduces a comprehensive formalism combining ab initio calculations and disorder modeling to study finite-temperature spin wave behavior in alloys.

Findings

Magnonic bandgap remains stable at high temperatures.

Disorder-induced damping is significantly smaller than Landau damping.

Magnon attenuation varies non-monotonically with impurity concentration.

Abstract

We study theoretically the influence of the temperature and disorder on the spin wave spectrum of the magnonic crystal Fe$_{1-c}$Co$_{c}$. Our formalism is based on the analysis of a Heisenberg Hamiltonian by means of the wave vector and frequency dependent transverse magnetic susceptibility. The exchange integrals entering the model are obtained from the \emph{ab initio} magnetic force theorem. The coherent potential approximation is employed to treat the disorder and random phase approximation in order to account for the softening of the magnon spectrum at finite temperatures. The alloy turns out to exhibit many advantageous properties for spintronic applications. Apart from high Curie temperature, its magnonic bandgap remains stable at elevated temperatures and is largely unaffected by the disorder. We pay particular attention to the attenuation of magnons introduced by the alloying. The damping turns out to be a non-monotonic function of the impurity concentration due to the non-trivial evolution of the value of exchange integrals with the Co concentration. The disorder induced damping of magnons is estimated to be much smaller than their Landau damping.