Unexpected structural and magnetic depth dependence of YIG thin films

TL;DR

This study uses polarized neutron reflectometry to reveal complex depth-dependent structural and magnetic properties in YIG thin films on different substrates, highlighting interfacial layers and their potential impact on spintronic effects.

Contribution

It provides detailed depth profiles of YIG thin films, identifying distinct interfacial layers and quantifying induced magnetism in Pt layers, which advances understanding of interface effects in spintronics.

Findings

Identification of a non-magnetic interfacial layer near GGG/YIG interface.

Detection of a thin, likely Y2O3, surface layer affecting magnetic properties.

Induced magnetism in Pt layers is less than 0.02 μB/atom.

Abstract

We report measurements on yttrium iron garnet (YIG) thin films grown on both gadolinium gallium garnet (GGG) and yttrium aluminium garnet (YAG) substrates, with and without thin Pt top layers. We provide three principal results: the observation of an interfacial region at the Pt/YIG interface, we place a limit on the induced magnetism of the Pt layer and confirm the existence of an interfacial layer at the GGG/YIG interface. Polarised neutron reflectometry (PNR) was used to give depth dependence of both the structure and magnetism of these structures. We find that a thin film of YIG on GGG is best described by three distinct layers: an interfacial layer near the GGG, around 5 nm thick and non-magnetic, a magnetic bulk phase, and a non-magnetic and compositionally distinct thin layer near the surface. We theorise that the bottom layer, which is independent of the film thickness, is caused by Gd diffusion. The top layer is likely to be extremely important in inverse spin Hall effect measurements, and is most likely Y2O3 or very similar. Magnetic sensitivity in the PNR to any induced moment in the Pt is increased by the existence of the Y2O3 layer; any moment is found to be less than 0.02 uB/atom.