Orientation-dependent stabilization of MgCr$_2$O$_4$ spinel thin films

TL;DR

This study demonstrates the first epitaxial growth of (111)-oriented MgCr₂O₄ spinel thin films, revealing orientation-dependent structural properties and potential for novel magnetic heterostructures.

Contribution

It introduces the first successful growth of (111)-oriented MgCr₂O₄ thin films and analyzes how growth orientation affects their structural and electronic properties.

Findings

(111) films are smoother and more crystalline than (001) films.

No measurable disorder or multivalency issues in either orientation.

Growth orientation is influenced by surface energy considerations.

Abstract

AB$_2$O$_4$ normal spinels with a magnetic B site can host a variety of magnetic and orbital frustrations leading to spin-liquid phases and field-induced phase transitions. Here we report the first epitaxial growth of (111)-oriented MgCr$_2$O$_4$ thin films. By characterizing the structural and electronic properties of films grown along (001) and (111) directions, the influence of growth orientation has been studied. Despite distinctly different growth modes observed during deposition, the comprehensive characterization reveals no measurable disorder in the cation distribution nor multivalency issue for Cr ions in either orientation. Contrary to a naive expectation, the (111) stabilized films exhibit a smoother surface and a higher degree of crystallinity than (001)-oriented films. The preference in growth orientation is explained within the framework of heteroepitaxial stabilization in connection to a significantly lower (111) surface energy. These findings open broad opportunities in the fabrication of 2D kagome-triangular heterostructures with emergent magnetic behavior inaccessible in bulk crystals.