# Manifestation of higher-order inter-granular exchange in magnetic recording media

## TL;DR

This study uses atomistic spin modeling to explore how impurity migration into grain boundaries affects higher-order exchange interactions in magnetic recording media, revealing the importance of biquadratic terms for accurate description.

## Contribution

It demonstrates the necessity of including biquadratic exchange terms to accurately model inter-granular coupling influenced by impurities in magnetic media.

## Key findings

- Biquadratic exchange term is needed at low impurity densities.
- Both exchange terms follow a power law decay with temperature.
- Unexpected energy minimum for in-plane magnetization observed.

## Abstract

Exchange coupling between magnetic grains is essential for maintaining the stability of stored information in magnetic recording media. Using an atomistic spin model, we have investigated the coupling between neighbouring magnetic grains where magnetic impurity atoms have migrated into the non-magnetic grain boundary. We find that when the impurity density is low a biquadratic term in addition to the bilinear term is required to properly describe the inter-granular exchange coupling. The temperature dependence both terms is found to follow a power law behaviour with the biquadratic exchange constant decaying faster than the bilinear. For increasing grain boundary thickness the inter-granular exchange is lower and decays faster with temperature. Further simulations of a grain at a bit boundary show an unexpected energy minimum for in-plane magnetisation which can only be reproduced using a biquadratic exchange term.