Coupled multiferroic domain switching in the canted conical spin spiral system Mn$_{2}$GeO$_{4}$

TL;DR

This study investigates the multiferroic properties of Mn$_{2}$GeO$_{4}$, revealing its unique double-Q conical magnetic structure and unconventional magnetoelectric couplings, including magnetic-field-driven reversal of polarization.

Contribution

It provides the first detailed analysis of multiferroic domains in Mn$_{2}$GeO$_{4}$ and introduces a phenomenological theory explaining its magnetoelectric coupling mechanisms.

Findings

Mn$_{2}$GeO$_{4}$ has a double-Q conical magnetic structure.

Magnetic-field can reverse ferroelectric polarization without changing spin-helicity.

The study establishes Mn$_{2}$GeO$_{4}$ as a simple multiferroic with coupled magnetic and electric properties.

Abstract

Despite remarkable progress in developing multifunctional materials, spin-driven ferroelectrics featuring both spontaneous magnetization and electric polarization are still rare. Among such ferromagnetic ferroelectrics are conical spin spiral magnets with a simultaneous reversal of magnetization and electric polarization that is still little understood. Such materials can feature various multiferroic domains that complicates their study. Here we study the multiferroic domains in ferromagnetic ferroelectric Mn$_{2}$GeO$_{4}$ using neutron diffraction, and show that it features a double-Q conical magnetic structure that, apart from trivial 180 degree commensurate magnetic domains, can be described by ferromagnetic and ferroelectric domains only. We show unconventional magnetoelectric couplings such as the magnetic-field-driven reversal of ferroelectric polarization with no change of spin-helicity, and present a phenomenological theory that successfully explains the magnetoelectric coupling. Our measurements establish Mn$_{2}$GeO$_{4}$ as a conceptually simple multiferroic in which the magnetic-field-driven flop of conical spin spirals leads to the simultaneous reversal of magnetization and electric polarization.