Polarization memory in the nonpolar magnetic ground state of multiferroic CuFeO2

TL;DR

This study reveals that CuFeO2 retains a polarization memory in its nonpolar magnetic ground state, allowing recovery of ferroelectric polarization upon re-entering the ferroelectric phase, driven by magnetic or thermal history effects.

Contribution

It demonstrates a robust polarization memory effect in CuFeO2's magnetic ground state, supported by Monte Carlo simulations suggesting helical domain walls as the underlying mechanism.

Findings

Memory effect persists without external bias.

Polarization can be recovered after magnetic or thermal cycling.

Memory is unaffected by domain state or applied stress.

Abstract

We investigate polarization memory effects in single-crystal CuFeO2, which has a magnetically-induced ferroelectric phase at low temperatures and applied B fields between 7.5 and 13 T. Following electrical poling of the ferroelectric phase, we find that the nonpolar collinear antiferromagnetic ground state at B = 0 T retains a strong memory of the polarization magnitude and direction, such that upon re-entering the ferroelectric phase a net polarization of comparable magnitude to the initial polarization is recovered in the absence of external bias. This memory effect is very robust: in pulsed-magnetic-field measurements, several pulses into the ferroelectric phase with reverse bias are required to switch the polarization direction, with significant switching only seen after the system is driven out of the ferroelectric phase and ground state either magnetically (by application of B > 13 T) or thermally. The memory effect is also largely insensitive to the magnetoelastic domain composition, since no change in the memory effect is observed for a sample driven into a single-domain state by application of stress in the [1-10] direction. On the basis of Monte Carlo simulations of the ground state spin configurations, we propose that the memory effect is due to the existence of helical domain walls within the nonpolar collinear antiferromagnetic ground state, which would retain the helicity of the polar phase for certain magnetothermal histories.