Gradual pressure-induced change in the magnetic structure of the non-collinear antiferromagnet Mn$_3$Ge

TL;DR

This study uses neutron diffraction to explore how hydrostatic pressure alters the magnetic structure of Mn$_3$Ge, revealing a transition from a non-collinear antiferromagnetic to a collinear ferromagnetic state with associated magnetoelastic effects.

Contribution

It provides the first detailed investigation of pressure-induced magnetic structure changes in Mn$_3$Ge, highlighting the gradual transformation and magnetoelastic coupling.

Findings

Magnetic structure transitions from coplanar to non-coplanar and then to collinear ferromagnetic with increasing pressure.

Magnetostriction effects accompany magnetic order changes, affecting the unit cell strain orientation.

Pressure induces a uniform out-of-plane spin canting in Mn$_3$Ge.

Abstract

By means of powder neutron diffraction we investigate changes in the magnetic structure of the coplanar non-collinear antiferromagnet Mn$_3$Ge caused by an application of hydrostatic pressure up to 5\phantom{ }GPa. At ambient conditions the kagom\'e layers of Mn atoms in Mn$_3$Ge order in a triangular 120$^{\circ}$ spin structure. Under high pressure the spins acquire a uniform out-of-plane canting, gradually transforming the magnetic texture to a non-coplanar configuration. With increasing pressure the canted structure fully transforms into the collinear ferromagnetic one. We observed that magnetic order is accompanied by a noticeable magnetoelastic effect, namely, spontaneous magnetostriction. The latter induces an in-plane magnetostrain of the hexagonal unit cell at ambient pressure and flips to an out-of-plane strain at high pressures in accordance with the change of the magnetic structure.