Magnetic field induced spin reorientation in the strongly anisotropic antiferromagnetic crystal LiCoPO4

It has been found experimentally that in the strongly anisotropic orthorhombic antiferromagnetic crystal LiCoPO4 (TN=21.7K) the destruction of antiferromagnetic order by a magnetic field directed along the antiferromagnetism axis H∥b occurs in steps by means of three phase transitions: two first-order transitions in the fields H1=118kOe, H2=224Oe and one second-order phase transition in the field H3=283kOe (T=1.7K). A section of magnetic fields (H2, H3) where the magnetization of the crystal varies almost linearly with the field was found. Possible magnetic structures formed in a magnetic field are discussed. The values of the exchange parameters are estimated.