Calculation of the high-frequency magnetic susceptibility tensor of a magnet

An algorithm for calculating nondiagonal components of the high-frequency magnetic susceptibility tensor of a magnet $\chi(\mathbf k,\omega)$ is developed which is based on a special representation of spin operators [1]. It is shown that the calculation of $\chi_{xy}(\mathbf k,\omega)$ and $\chi_{yx}(\mathbf k,\omega)$ in this representation is reduced to calculating one-particle, Green functions of quasiparticles and certain coefficients which are of the form of series similar to the series for the mass operator of the one-particle Green functions.