Magnon properties of random alloys

TL;DR

This study investigates how atomic disorder in Fe-Ni, Co-Ni, and Fe-Co alloys influences magnon properties like spin stiffness, Curie temperature, and magnon spectrum, revealing system-dependent effects with potential technological implications.

Contribution

It provides a detailed analysis of disorder effects on magnon spectra in random alloys using combined electronic structure and spin dynamics simulations, highlighting differences among alloy systems.

Findings

Disorder causes significant broadening of magnon spectra in Fe-Ni alloys.

Fe-Co alloys exhibit sharp magnon branches and high Curie temperatures.

Low Gilbert damping (~0.0007) observed in Co-rich Fe-Co alloys at room temperature.

Abstract

We study magnon properties in terms of spin stiffness, Curie temperatures and magnon spectrum of Fe-Ni, Co-Ni and Fe-Co random alloys using a combination of electronic structure calculations and atomistic spin dynamics simulations. Influence of the disorder are studied in detail by use of large supercells with random atomic arrangement. It is found that disorder affects the magnon spectrum in vastly different ways depending on the system. Specifically, it is more pronounced in Fe-Ni alloys compared to Fe-Co alloys. In particular, the magnon spectrum at room temperature in Permalloy (Fe$_{20}$Ni$_{80}$) is found to be rather diffuse in a large energy interval while in Fe$_{75}$Co$_{25}$ it forms sharp branches. Fe-Co alloys are very interesting from a technological point of view due to the combination of large Curie temperatures and very low calculated Gilbert damping of $\sim$0.0007 at room temperature for Co concentrations around 20--30\%.