Anisotropy of antiferromagnetic 180° domains in magnetoelectric LiMPO_4(M= Fe, Co, Ni)

摘要

An unusual variety of magnetic, magnetoelectric and ferrotoroidic properties was observed inthe lithium-orthophosphates LiMPO4 with M = Fe, Co, Ni by optical second harmonic generation. In spiteof a largely similar magnetic and crystallographic structure the compounds exhibit pronounced differencesin the topology of antiferromagnetic 180° domains. In LiCoPO4 the antiferromagnetic domains coexistwith ferrotoroidic, i.e., magnetic vortex domains. For LiNiPO4 it was shown that the weak ferrimagneticmoment of the LiMPO4 compounds along the spin direction is rigidly coupled to the AFM order parameterso that the sign of the magnetoelectric effect is reversed by a magnetic field only. Further effects of a staticmagnetic field on the system are discussed.