Ground state of a two-sublattice anisotropic ferromagnet in a magnetic field

The ground state of a classical ferromagnet with the noncollinear single-ion anisotropy axes of the two sublattices and antisymmetric and anisotropic symmetric exchanges between the sublattices has been considered in a magnetic field applied in the hard magnetic directions of the crystal. The threshold conditions on the anisotropic interactions parameters determined the ground state among the three possible magnetic phases have been obtained. Depended on the type of the ground state and field direction the transition between the phases occurs as a phase transition first or second order. The value of the antisymmetric exchange above that the reorientation between two noncollinear phases is terminated by the second order phase transition depends on the angle between the local easy axes and the value of single-ion anisotropy. The field dependences of the magnetization and susceptibility have been calculated for the different ground states. The comparison with the results of the magnetic measurements in the highly anisotropic ferromagnet PbMnBO$_{4}$ has been made.