Perspective on Epitaxial NiCo2O4 Film as an Emergent Spintronic Material: Magnetism and Transport Properties

TL;DR

This paper reviews recent progress in epitaxial NiCo2O4 thin films, highlighting their unique magnetic and transport properties, underlying mechanisms, and potential for nanoscale spintronic device applications.

Contribution

It provides a comprehensive analysis of the intrinsic physical properties and tunability of epitaxial NiCo2O4 films, emphasizing the effects of growth conditions and crystal structure on magnetic and transport phenomena.

Findings

Perpendicular magnetic anisotropy explained by spin-lattice coupling.

Growth conditions influence cation stoichiometry and valence states.

Magnetotransport anomalies linked to Berry phase and impurity scattering.

Abstract

The ferrimagnetic inverse spinel NiCo2O4 has attracted extensive research interests for its versatile electrochemical properties, robust magnetic order, high conductivity, and fast spin dynamics, as well as its highly tunable nature due to the closely coupled charge, spin, orbital, lattice, and defect effects. Single-crystalline epitaxial thin films of NiCo2O4 present a model system for elucidating the intrinsic physical properties and strong tunability, which are not viable in bulk single crystals. In this perspective, we discuss the recent advances in epitaxial NiCo2O4 thin films, focusing on understanding its unusual magnetic and transport properties in light of crystal structure and electronic structure. The perpendicular magnetic anisotropy in compressively strained NiCo2O4 films is explained by considering the strong spin-lattice coupling, particularly on Co ions. The prominent effect of growth conditions reveals the complex interplay between the crystal structure, cation stoichiometry, valence state, and site occupancy. NiCo2O4 thin films also exhibit various magnetotransport anomalies, including linear magnetoresistance and sign change in anomalous Hall effect, which illustrate the competing effects of band intrinsic Berry phase and impurity scattering. The fundamental understanding of these phenomena will facilitate the functional design of NiCo2O4 thin films for nanoscale spintronic applications.