# The influence of anti-site defects and stacking faults on the magneto crystalline anisotropy of FePt

## TL;DR

This study uses density functional theory to analyze how anti-site defects and stacking faults affect the magnetic anisotropy energy of FePt, reconciling theoretical predictions with experimental results.

## Contribution

It demonstrates that anti-site defects significantly reduce FePt's magnetic anisotropy energy, explaining discrepancies between ideal calculations and experimental data.

## Key findings

- Anti-site defects lower the MAE of FePt.
- Stacking faults have a lesser impact on MAE.
- Disorder explains the difference between theoretical and experimental MAE.

## Abstract

We present density functional theory (DFT) calculations of the magnetic anisotropy energy (MAE) of FePt, which is of great interest for magnetic recording applications. Our data, and the majority of previously calculated results for perfectly ordered crystals, predict an MAE of $\sim 3.0$ meV per formula unit, which is significantly larger than experimentally measured values. Analyzing the effects of disorder by introducing stacking faults (SFs) and anti site defects (ASDs) in varying concentrations we are able to reconcile calculations with experimental data and show that even a low concentration of ASDs are able to reduce the MAE of FePt considerably. Investigating the effect of exact exchange and electron correlation within the adiabatic-connection dissipation fluctuation theorem in the random phase approximation (ACDFT-RPA) reveals a significantly smaller influence on the MAE. Thus the effect of disorder, and more specifically ASDs, is the crucial factor in explaining the deviation of common DFT calculations of FePt to experimental measurements.