Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy

TL;DR

This study investigates how interface effects influence the orbital magnetic moments in various magnetic heterostructures, revealing element-specific contributions and the role of oxidation states in ultrathin films.

Contribution

It provides new insights into the interface orbital magnetic moments and their dependence on layer thickness and oxidation states in different heterostructures.

Findings

Interface orbital moments vary with layer thickness and material.

Oxidized Co states contribute to interface orbital moments.

Element-specific interface contributions are identified.

Abstract

We have studied the magnetic layer thickness dependence of the orbital magnetic moment in magnetic heterostructures to identify contributions from interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlO$_x$ and Pt/Co/Pt, which possess significant interface contribution to the perpendicular magnetic anisotropy, are studied as model systems. X-ray magnetic circular dichroism spectroscopy is used to evaluate the relative orbital moment, i.e. the ratio of the orbital to spin moments, of the magnetic elements constituting the heterostructures. We find that the relative orbital moment of Co in Pt/Co/Pt remains constant against its thickness whereas the moment increases with decreasing Co layer thickness for Pt/Co/AlO$_x$, suggesting that a non-zero interface orbital moment exists for the latter system. For Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray absorption spectra shows that a particular oxidized Co state in Pt/Co/AlO$_x$, absent in other heterosturctures, may give rise to the interface orbital moment in this system. These results show element specific contributions to the interface orbital magnetic moments in ultrathin magnetic heterostructures.