Pressure effect on magnetism and multiferroicity inMn2GeO4

Abstract

The effect of high pressure exceeding 6 GPa on magnetism and multiferroicity was investigated for the olivine ${\text{Mn}}_{2}$${\text{GeO}}_{4}$ that shows successive magnetic transitions at ambient pressure and a ferroelectric ground state driven by spin-spiral order. We measured heat capacity, dielectric constant, and electric polarization at various pressures using a diamond anvil cell. The pressure evolution of the magnetic structures was also investigated by powder neutron diffraction measurements using a Paris-Edinburgh press. We found that all of the magnetic transition temperatures are enhanced monotonically by applying pressure. Furthermore, the spin-driven ferroelectricity persists up to about 6 GPa but suddenly vanishes by 6.3 GPa. A consistent description of all data is achieved if an incommensurate-commensurate phase transition occurs with pressurization and causes the suppression of ferroelectricity. We discuss the origin of the observed pressure effects on the magnetism and multiferroicity in ${\text{Mn}}_{2}$${\text{GeO}}_{4}$ in terms of a pressure-induced change in the superexchange magnetic interactions.