# Spin wave stiffness and exchange stiffness of doped permalloy via ab-initio calculation

## TL;DR

This study uses ab-initio calculations to analyze how doping with different elements affects the spin wave and exchange stiffness in permalloy, revealing that hybridization, not impurity polarizability, governs these properties.

## Contribution

It demonstrates that impurity-host hybridization, rather than polarizability, primarily influences the stiffness changes due to doping in permalloy, based on first-principles calculations.

## Key findings

- Doping alters spin wave and exchange stiffness via hybridization.
- Nearest-neighbor exchange coupling suffices to describe stiffness trends.
- Results align well with previous experimental data.

## Abstract

The way doping affects the spin wave stiffness and the exchange stiffness of permalloy (Py) is investigated via ab-initio calculations, using the Korringa-Kohn-Rostoker (KKR) Green function formalism. By considering various types of dopants of different nature (V, Gd, and Pt), we are able to draw general conclusions. To describe the trends of the stiffness with doping is it sufficient to account for the exchange coupling between nearest neighbors. The polarizability of the impurities is not an important factor for the spin wave stiffness. Rather, the decisive factor is the hybridization between the impurity and the host states as reflected by changes in the Bloch spectral function. Our theoretical results agree well with earlier experiments.