Electric polarization memory effect in a magnetoelectric multiferroic CuFe1−xGaxO2

Abstract

Magnetic oxide CuFeO2 is a magnetoelectric multiferroic with new type of spin–polarization coupling different from that in the spin-current mechanism, where magnetic field-induced or nonmagnetic impurity-induced proper helical magnetic ordering generates a spontaneous electric polarization parallel to the helical axis. Using a CuFe1−xGaxO2 sample with x=0.035, in which the single ferroelectric phase is realized below TN∼8 K in zero magnetic field unlike CuFe1−xAlxO2, we have performed pyroelectric current, thermally stimulated current (TSC) and polarized neutron diffraction measurements to study a memory effect that the electric polarization is partially preserved even for 2nd-cooling from above TN without poling electric field. It was found that the charge trapped during 1st-cooling with poling electric field, which is released as TSC on heating, plays an important role in the memory effect.