Magnetoelectric Effect in Antiferromagnets with Honeycomb Structures

Magnetic and magnetoelectric (ME) properties of honeycomb lattice antiferromagnets M4Nb2O9 (M = Mn, Co, Mn1-xCox ) were investigated. Mn4Nb2O9 show colinear antiferromagnetic order and ME effect in the temperature range below TN = 109 K. The electric polarization induced by ME effect shows a maximum at 90 K, which reflects the temperature dependence of the magnetic susceptibility along the c axis. Magnetization measurements of Co4Nb2O9 under an applied electric field revealed that the magnitude of magnetization varies in proportion to the applied electric field. Changes in magnetic transition temperature and magnetic anisotropy were investigated for (Mn1-xCox )4Nb2O9 single crystals. It was found that the magnetic transition temperature changes linearly with composition, while the magnetic anisotropy changes by replacing Mn with a small amount of Co.