Exchange anisotropy-driven noncollinear magnetism and magnetic transitions in MnTiO3 ilmenite

TL;DR

This study reveals multiple magnetic transitions and unconventional spin interactions in MnTiO3, driven by exchange anisotropy and lattice distortions, leading to complex noncollinear magnetic structures.

Contribution

It provides the first neutron scattering evidence of noncollinear magnetism and multiple magnetic phases in MnTiO3, highlighting the role of exchange anisotropy and lattice buckling.

Findings

G-type AFM order at 63 K

Emergence of noncollinear structure near 42 K

Exchange interactions include Heisenberg, Dzyaloshinskii-Moriya, and ferromagnetic couplings

Abstract

Evidence for multiple magnetic transitions and unconventional spin exchange interactions in the ilmenite insulator MnTiO3 is provided via neutron scattering. On cooling, while G-type antiferromagnetic (AFM) order sets in first at 63 K with a k1 = (000) characteristic wave vector, a weaker second magnetic transition with k2 = (00 3/2 ) appears near 42 K, giving rise to a noncollinear structure. Intrinsic buckling of the honeycomb lattice along c creates bond anisotropy and a distorted crystal field that can lead to exchange paths that modulate orbital overlap and spin-orbit coupling. The inelastic spectrum is best described by magnetic exchange anisotropy that breaks the local symmetry of the honeycomb, with competing AFM Heisenberg, Dzyaloshinskii-Moriya and alternate intra-planar ferromagnetic (FM) interactions, that may yield a weakly-coupled ladder system.