Stress-induced magnetic domain selection reveals a conical ground state for the multiferroic phase of Mn2GeO4

TL;DR

This study investigates the magnetic and ferroelectric properties of Mn2GeO4 under high pressure, revealing a conical magnetic ground state induced by stress and clarifying the pressure-dependent suppression of ferroelectricity.

Contribution

The paper demonstrates that a conical magnetic ground state exists in Mn2GeO4 and shows how uniaxial stress influences magnetic domain selection, advancing understanding of multiferroic phase behavior under pressure.

Findings

Incommensurate spiral magnetic component remains stable up to 5.1 GPa.

High pressure suppresses ferroelectricity via a structural transition.

Uniaxial stress induces a specific magnetic domain selection, revealing a conical ground state.

Abstract

At ambient pressure (P) and below 5.5 K, olivine-type Mn2GeO4 hosts a multiferroic (MF) phase where a multicomponent, i.e., multi-k magnetic order generates spontaneous ferromagnetism and ferroelectricity (FE) along the c axis. Under high P the FE disappears above 6 GPa, yet the P evolution of the magnetic structure remained unclear based on available data. Here we report high P single crystal neutron diffraction experiments in theMF phase at T = 4.5 K.We observe clearly that the incommensurate spiral component of the magnetic order responsible for FE varies little with P up to 5.1 GPa. With support from high P synchrotron x-ray diffraction measurements at room temperature (T), the P driven suppression of FE is proposed to occur as a consequence of a crystal structure transition away from the olivine structure. In addition, in the low T neutron scattering experiments an emergent nonhydrostatic P component, i.e., a uniaxial stress, leads to the selection of certain multi-k domains. We use this observation to deduce a double-k conical magnetic structure for the ambient P ground state, this being a key ingredient for a model description of the MF phase.