Exchange coupling and magnetic anisotropy at Fe/FePt interfaces

TL;DR

This study uses relativistic first principles calculations to analyze how Fe/FePt interfaces influence exchange interactions and magnetic anisotropy, revealing reduced interfacial exchange and MAE effects in multilayer systems.

Contribution

It provides detailed insights into the impact of Fe/FePt interfaces on magnetic properties, highlighting the importance of interface relaxation and exchange interactions.

Findings

Interfacial Fe layer reduces exchange coupling with soft Fe phase.

Fe/FePt interfaces decrease the perpendicular MAE of the system.

Relaxation marginally mitigates the reduction in MAE and exchange at interfaces.

Abstract

We perform fully relativistic first principles calculations of the exchange interactions and the magnetocrystalline anisotropy energy (MAE) in an Fe/FePt/Fe sandwich system in order to elucidate how the presence of Fe/FePt (soft/hard magnetic) interfaces impacts on the magnetic properties of Fe/FePt/Fe multilayers. Throughout our study we make comparisons between a geometrically unrelaxed system and a geometrically relaxed system. We observe that the Fe layer at the Fe/FePt interface plays a crucial role inasmuch its (isotropic) exchange coupling to the soft (Fe) phase of the system is substantially reduced. Moreover, this interfacial Fe layer has a substantial impact on the MAE of the system. We show that the MAE of the FePt slab, including the contribution from the Fe/FePt interface, is dominated by anisotropic inter-site exchange interactions. Our calculations indicate that the change in the MAE of the FePt slab with respect to the corresponding bulk value is negative, i.e., the presence of Fe/FePt interfaces appears to reduce the perpendicular MAE of the Fe/FePt/Fe system. However, for the relaxed system, this reduction is marginal. It is also shown that the relaxed system exhibits a reduced interfacial exchange. Using a simple linear chain model we demonstrate that the reduced exchange leads to a discontinuity in the magnetisation structure at the interface.