Intrinsic Exchange Bias from Interfacial Reconstruction in an Epitaxial NixCoyFe3-x-yO4(111)/{\alpha}-Al2O3(0001) Thin Film Family

TL;DR

This study demonstrates that intrinsic exchange bias in Ni-Co-Fe spinel oxide films on Al2O3 substrates arises from interfacial reconstruction forming a CoO layer, with tunability via stoichiometry and interface engineering.

Contribution

It reveals that intrinsic exchange bias is a general phenomenon caused by interfacial reconstruction in (Ni, Co, Fe)-based spinel oxides on Al2O3, highlighting a new interface engineering strategy.

Findings

Intrinsic exchange bias correlates with Co concentration.

Interfacial reconstruction leads to CoO formation.

Exchange bias tunability via stoichiometry.

Abstract

Intrinsic exchange bias is known as the unidirectional exchange anisotropy that emerges in a nominally single-component ferro-(ferri-)magnetic system. In this work, with magnetic and structural characterizations, we demonstrate that intrinsic exchange bias is a general phenomenon in (Ni, Co, Fe)-based spinel oxide films deposited on {\alpha}-Al2O3(0001) substrates, due to the emergence of a rock-salt interfacial layer consisting of antiferromagnetic CoO from interfacial reconstruction. We show that in NixCoyFe3-x-yO4(111)/{\alpha}-Al2O3(0001) films, intrinsic exchange bias and interfacial reconstruction have consistent dependences on Co concentration y, while the Ni and Fe concentration appears to be less important. This work establishes a family of intrinsic exchange bias materials with great tunability by stoichiometry and highlights the strategy of interface engineering in controlling material functionalities.