Exchange bias and interface electronic structure in Ni/Co3O4(011)

TL;DR

This study investigates the exchange bias effect in Ni/Co3O4(011), revealing that the effect persists above the bulk Co3O4 Neel temperature due to interfacial CoO formation, not intrinsic properties of Co3O4.

Contribution

It demonstrates that the exchange bias in Ni/Co3O4 systems arises from interfacial CoO formation rather than the intrinsic properties of Co3O4.

Findings

Exchange bias persists above Co3O4 Neel temperature.

Interfacial CoO formation causes the exchange bias.

The effect varies with surface roughness and temperature.

Abstract

A detailed study of the exchange bias effect and the interfacial electronic structure in Ni/Co3O4(011) is reported. Large exchange anisotropies are observed at low temperatures, and the exchange bias effect persists to temperatures well above the Neel temperature of bulk Co3O4, of about 40 K: to ~80 K for Ni films deposited on well ordered oxide surfaces, and ~150 K for Ni films deposited on rougher Co3O4 surfaces. Photoelectron spectroscopy measurements as a function of Ni thickness show that Co reduction and Ni oxidation occur over an extended interfacial region. We conclude that the exchange bias observed in Ni/Co3O4, and in similar ferromagnetic metallic/Co3O4 systems, is not intrinsic to Co3O4 but rather due to the formation of CoO at the interface.