Anisotropic Exchange Interactions in a Ferromagnet PbMnBO4

The field dependence of the magnetization along the hard axes in a four-sublattice ferromagnet PbMnBO₄ is calculated by the numerical minimization of the ground state energy in the approximation of classical magnetic moments. The parameters of anisotropic interactions—the second-order single-ion anisotropy constants, the magnitude and direction of the antisymmetric exchange vector, and the symmetric anisotropic exchange tensor—are obtained by a comparison with experimental magnetization curves. The direction of the Dzyaloshinskii–Moriya interaction vector is close to the orthorhombic c axis. The symmetric exchange tensor has an almost uniaxial form with the easy axis perpendicular to the antisymmetric exchange vector. Changes in the energy of each anisotropic interaction during magnetization reorientation are calculated.