Orbital-spin order and the origin of structural distortion in MgTi$_2$O$_4$

TL;DR

This paper investigates the electronic, magnetic, and structural properties of MgTi$_2$O$_4$, revealing a canted orbital-spin ordered state that explains its dimerized phase and structural distortions through electron interactions.

Contribution

It introduces a comprehensive LDA+U based model showing how orbital order stabilizes the magnetic ground state and induces structural distortions in MgTi$_2$O$_4$, advancing understanding of frustrated materials.

Findings

Identification of a canted orbital-spin ordered state

Orbital order stabilizes the magnetic ground state

Structural distortions are derived from the cubic structure

Abstract

We analyze electronic, magnetic, and structural properties of the spinel compound MgTi$_2$O$_4$ using the local density approximation+U method. We show how MgTi$_2$O$_4$ undergoes to a canted orbital-spin ordered state, where charge, spin and orbital degrees of freedom are frozen in a geometrically frustrated network by electron interactions. In our picture orbital order stabilize the magnetic ground state and controls the degree of structural distortions. The latter is dynamically derived from the cubic structure in the correlated LDA+U potential. Our ground-state theory provides a consistent picture for the dimerized phase of MgTi$_2$O$_4$, and might be applicable to frustrated materials in general.