# Magnetic anisotropy in Permalloy: hidden quantum mechanical features

## TL;DR

This study uses relativistic first principles calculations to uncover the microscopic origins of Permalloy's low magnetic anisotropy, revealing local atomic variations and their implications for magnetic behavior.

## Contribution

It demonstrates that local atomic anisotropy in Permalloy can be significantly larger than the bulk, providing new insights into its magnetic properties and quantum features.

## Key findings

- Local atomic anisotropy can be 5-10 times larger than elemental Fe or Ni.
- Multiple easy axis directions depend on local composition.
- Permalloy's ferromagnetism is maintained by exchange energy despite low anisotropy.

## Abstract

By means of relativistic, first principles calculations, we investigate the microscopic origin of the vanishingly low magnetic anisotropy of Permalloy, here proposed to be intrinsically related to the local symmetries of the alloy. It is shown that the local magnetic anisotropy of individual atoms in Permalloy can be several orders of magnitude larger than that of the bulk sample, and 5-10 times larger than that of elemental Fe or Ni. We, furthermore, show that locally there are several easy axis directions that are favored, depending on local composition. The results are discussed in the context of perturbation theory, applying the relation between magnetic anisotropy and orbital moment. Permalloy keeps its strong ferromagnetic nature due to the exchange energy to be larger than the magnetocrystalline anisotropy. Our results shine light on the magnetic anisotropy of permalloy and of magnetic materials in general, and in addition enhance the understanding of pump-probe measurements and ultrafast magnetization dynamics.