Magnetic excitations in an anharmonic ferromagnetic crystal

An investigation is made of the spectrum of magnetic excitations in an anharmonic ferromagnet in the framework of the Heisenberg model with allowance for the spin-phonon interaction of all orders in the displacements of the atoms. An exact representation is obtained for the mass operator of the two-time Green's function of the transverse spin components and an approximate expression for it is considered in the second order in the renormalized spinphonon and spin-spin interactions.