Theory of perpendicular magnetocrystalline anisotropy in Fe/MgO (001)

TL;DR

This study reveals that perfect epitaxy, rather than Fe-O hybridization, is the main factor behind large perpendicular magnetocrystalline anisotropy in Fe/MgO (001), with detailed analysis of electronic contributions.

Contribution

It demonstrates that epitaxial quality is more crucial than Fe-O hybridization for PMCA, providing new insights into the origin of magnetic anisotropy in Fe/MgO interfaces.

Findings

Perfect epitaxy enhances PMCA in Fe/MgO.

Fe-O hybridization is not the main cause of large PMCA.

Surface and interface Fe layers contribute similarly to PMCA.

Abstract

The origin of large perpendicular magneto-crystalline anisotropy (PMCA) in Fe/MgO (001) is revealed by comparing Fe layers with and without the MgO. Although Fe-O $p$-$d$ hybridization is weakly present, it cannot be the main origin of the large PMCA as claimed in previous study. Instead, perfect epitaxy of Fe on the MgO is more important to achieve such large PMCA. As an evidence, we show that the surface layer in a clean free-standing Fe (001) dominantly contributes to $E_{MCA}$, while in the Fe/MgO, those by the surface and the interface Fe layers contribute almost equally. The presence of MgO does not change positive contribution from $\langle xz|\ell_Z|yz\rangle$, whereas it reduces negative contribution from $\langle z^2|\ell_X|yz\rangle$ and $\langle xy|\ell_X|xz,yz\rangle$.