Normal modes and relaxation processes in magnetically ordered materials with single-ion anisotropy

The method of diagonalizing a spin Hamiltonian proposed earlier by the authors [8] is generalized to systems with nonequidistant spectrum. The treatment is given in the framework of the diagram technique for operators of a universal basis [6, 7] for the example of the nuclear subsystem of an antiferromagnet with quadrupole interaction, which plays the part of single-site axial anisotropy. The spectrum of nuclear spin waves with quadrupole splitting is found and the relaxation frequencies of these waves due to their scattering by thermal fluctuations in the longitudinal component of the nuclear spins are determined.