Interfacial and Surface Magnetism in Epitaxial NiCo2O4(001)/MgAl2O4 Films

TL;DR

This study investigates the magnetic properties of epitaxial NiCo2O4 films on MgAl2O4 substrates, revealing interfacial effects, layer-specific behaviors, and the influence of film thickness on magnetic coupling and anisotropy.

Contribution

It provides a detailed analysis of interfacial and surface magnetism in NiCo2O4 films, highlighting the role of interfacial diffusion and finite-scaling theory in magnetic behavior.

Findings

Interfacial layer couples antiferromagnetically to the optimal layer.

Magnetic properties depend on film thickness and interfacial diffusion.

Finite-scaling theory describes the thickness dependence of the magnetic layer.

Abstract

NiCo2O4 (NCO) films grown on MgAl2O4 (001) substrates have been studied using magnetometry, x-ray magnetic circular dichroism (XMCD) based on x-ray absorption spectroscopy, and spin-polarized inverse photoemission spectroscopy (SPIPES) with various thickness down to 1.6 nm. The magnetic behavior can be understood in terms of a layer of optimal NCO and an interfacial layer (1.2+/- 0.1 nm), with a small canting of magnetization at the surface. The thickness dependence of the optimal layer can be described by the finite-scaling theory with a critical exponent consistent with the high perpendicular magnetic anisotropy. The interfacial layer couples antiferromagnetically to the optimal layer, generating exchange-spring styled magnetic hysteresis in the thinnest films. The non-optimal and measurement-speed-dependent magnetic properties of the interfacial layer suggest substantial interfacial diffusion.