Strong magnon softening in tetragonal FeCo compounds

TL;DR

This study uses ab initio methods to analyze magnon spectra in tetragonal FeCo compounds, revealing strong magnon softening and damping effects influenced by tetragonal distortion, with implications for magnetic recording technology.

Contribution

It provides the first detailed ab initio analysis of magnon spectra in tetragonal FeCo compounds considering different c/a ratios, highlighting the impact of structural distortion on magnon properties.

Findings

Magnons are strongly damped at short wavelengths in all studied compounds.

Tetragonal distortion significantly softens magnons, reducing the magnon stiffness constant D.

FeCo/Rh exhibits promising properties for perpendicular magnetic recording due to soft magnons and high magnetic anisotropy.

Abstract

Magnons play an important role in fast precessional magnetization reversal processes serving as a heat bath for dissipation of the Zeeman energy and thus being responsible for the relaxation of magnetization. Employing \emph{ab initio} many-body perturbation theory we studied the magnon spectra of the tetragonal FeCo compounds considering three different experimental $c/a$ ratios, $c/a=$1.13, 1.18, and 1.24 corresponding to FeCo grown on Pd, Ir, and Rh, respectively. We find that for all three cases the short-wave-length magnons are strongly damped and tetragonal distortion gives rise to a significant magnon softening. The magnon stiffness constant $D$ decreases almost by a factor of two from FeCo/Pd to FeCo/Rh. The combination of soft magnons together with the giant magnetic anisotropy energy suggests FeCo/Rh to be a promising material for perpendicular magnetic recording applications.