The magnetoelectric effect in single-crystal LiCoPO4 (TN = 21.8 K) is studied in strong pulsed magnetic fields which destroy the antiferromagnetic structure of the crystal spin ordering. The electric polarization along the crystallographic a axis induced by a magnetic field H||b is measured. New features of the electric polarization in a magnetic field are found, including a spike in the polarization near the field for the first magnetic transition at H1 = 123 kOe, a recovery of the electric polarization at the second magnetic transition H2 = 210 kOe, and a gradual reduction to zero on approaching the third transition at H3 = 263 kOe. Various possible magnetic structures in the high field phases are examined which are consistent with their magnetization and electric polarization. The observed linear dependence of the polarization on field strength in the initial antiferromagnetic phase and the vanishing of the polarization in the first high-field phase are in good agreement with previous studies of the magnetoelectric effect in LiCoPO4 [Wiegelmann et al., Ferroelectrics 161, 147 (1994); H. Wiegelman, Ph.D. thesis (University of Konstanz, Konstanz, 1995)].

The results of magnetization studies of the magnetoelectric antiferromagnetic LiNiPO4 single crystal in a pulse magnetic field with geometrical configuration H c are presented. The investigations have shown that a breakdown of the AFM state of LiNiPO4 in the magnetic field occurs by several stages. Temperature dependences of critical field values in the range 1.4 K -21 K are obtained.PACS : 75.50.Ee, 75.30.Kz

The magnetoelectric effect in single-crystal antiferromagnetic LiNiPO4 (TN = 29.8 K) is studied in pulsed magnetic fields up to 28 T. The electric polarization along the crystallographic axis a induced by a magnetic field H||c is measured. It is found that electric polarization develops in a low-field phase I (fields from 0 to 13 T) and a high-field phase V (20–21.5 T). In the low-field phase, the electric polarization has both linear and pronounced cubic dependences on the field.