Perpendicular magnetic anisotropy in Pt/Co-based full Heusler alloy/MgO thin films structures

TL;DR

This study investigates the origins of perpendicular magnetic anisotropy in ultrathin Pt/Co-based full Heusler alloy/MgO films, revealing interdiffusion effects and interface engineering as key factors influencing magnetic properties for spintronic applications.

Contribution

It demonstrates that interdiffusion and interface composition actively influence PMA in Heusler/MgO structures, challenging the notion that PMA is solely an intrinsic property.

Findings

Ultrathin Heusler films exhibit strong PMA without magnetic annealing.

Interdiffusion at the interface creates a CoFe-rich layer affecting magnetic behavior.

Choice of underlayer material modulates interdiffusion and PMA strength.

Abstract

Perpendicular magnetic anisotropy (PMA) in ultrathin magnetic structures is a key ingredient for the development of electrically controlled spintronic devices. Due to their relatively large spin-polarization, high Curie temperature and low Gilbert damping the Co-based full Heusler alloys are of special importance from a scientific and applications point of view. Here, we study the mechanisms responsible for the PMA in Pt/Co-based full Heusler alloy/MgO thin films structures. We show that the ultrathin Heusler films exhibit strong PMA even in the absence of magnetic annealing. By means of ferromagnetic resonance experiments, we demonstrate that the effective magnetization shows a two-regime behavior depending on the thickness of the Heusler layers. Using Auger spectroscopy measurements, we evidence interdiffusion at the underlayer/Heusler interface and the formation of an interfacial CoFe-rich layer which causes the two-regime behavior. In the case of the ultrathin films, the interfacial CoFe-rich layer promotes the strong PMA through the electronic hybridization of the metal alloy and oxygen orbitals across the ferromagnet/MgO interface. In addition, the interfacial CoFe-rich layer it is also generating an increase of the Gilbert damping for the ultrathin films beyond the spin-pumping effect. Our results illustrate that the strong PMA is not an intrinsic property of the Heusler/MgO interface but it is actively influenced by the interdiffusion, which can be tuned by a proper choice of the underlayer material, as we show for the case of the Pt, Ta and Cr underlayers.