Ferroelectricity induced by incommensurate-commensurate magnetic phase transition in multiferroic HoMn₂O₅

Neutron diffraction measurements under high magnetic fields in multiferroic HoMn₂O₅ have revealed a clear relationship between microscopic magnetism and field-induced ferroelectricity. The applied magnetic field induces a first-order phase transition from an incommensurate magnetic order to a commensurate magnetic order, where a spontaneous electric polarization occurs. The one-to-one correspondence between the magnetic phase diagram and the dielectric phase diagram under magnetic field clearly indicates that the electric polarization is magnetically induced and the commensurate magnetic structure is indispensable to the ferroelectricity in the multiferroic RMn₂O₅ system.