Multiferroicity on the Zigzag-Chain Antiferromagnet MnWO4 in High Magnetic Fields

Abstract

The electric polarization and magnetization of the zigzag-chain antiferromagnet MnWO 4 were measured in high pulsed magnetic fields of up to 53 T for the three principal directions x , y , and z , where x corresponds to the easy axis and y is the b * -direction. In addition to the AF1, AF2, and HF phases already known, two magnetic phases, IV and V, successively appear in high magnetic fields for B ∥ x at 4.2 K. We found that phase IV is ferroelectric with the electric polarization P parallel to the b * -axis, similar to the AF2 phase. It is also confirmed that phase IV is continuously connected to the previously reported X phase for the B ∥ y axis by changing the field direction. Interestingly, the successive field-induced phase transitions AF2–HF–IV in B ∥ x at a low temperature revealed that the signs of P ∥ b * for AF2 and phase IV are always opposite each other, in spite of the intervening paraelectric HF phase extending to over 20 T. This result implies that an unusual memory effect is present in th...