Spin Canting and Orbital Order in Spinel Vanadate Thin Films

TL;DR

This study investigates how epitaxial growth and structural tuning of CoV$_2$O$_4$ thin films influence their magnetic and orbital properties, revealing a strain-induced transition to a non-collinear magnetic ground state and increased spin canting.

Contribution

It demonstrates how epitaxial strain alters the magnetic anisotropy and ground state of CoV$_2$O$_4$ thin films, contrasting with bulk behavior and revealing new spin reorientation phenomena.

Findings

Structural symmetry lowering induces a different low-temperature magnetic state.

A 90 K transition involves a spin reorientation from [001] to [110].

V-spins exhibit increased canting angles under strain.

Abstract

We report on the epitaxial film growth and characterization of CoV$_2$O$_4$, a near-itinerant spinel vanadate, grown on (001) SrTiO$_3$. The symmetry lowering of the unit cell from cubic in the bulk to orthorhombic in the films results in dramatic differences in the magnetic anisotropy compared to bulk, as determined from structural and magnetic characterization. Bulk cubic CoV$_2$O$_4$ has been found to defy predictions by showing orbital degeneracy seemingly lasting to very low temperatures, with only small anomalies in magnetization and neutron experiments signaling a possible spin/orbital glass transition at T = 90 K. In epitaxial thin films presented in this paper, structurally tuning the CoV$_2$O$_4$ away from cubic symmetry leads to a completely different low temperature non-collinear ground state. Via magnetization and neutron scattering measurements we show that the 90 K transition is associated with a major spin reorientation away from the ferrimagnetic easy axis [001] to the [110] direction. Furthermore, the V-spins cant away from this direction with extracted perpendicular moments providing evidence of a larger canting angle compared to bulk. This result indicates that compressive strain pushes the system deeper into the insulating state, i.e., away from the localized - itinerant crossover regime.