Abstract
AbstractThe method of causal GREEN'S functions is used to derive equations and boundary conditions of non‐equilibrium correlation functions which describe spin wave like elementary excitations in a HEISENBERG ferromagnet with dipolar coupling influenced by a r. f. magnetic field parallel to the d.c. field. Starting with a matrix 𝔊 of four GREEN'S functions each containing two PAULI operators, by means of its functional equation a perturbation calculation is developed to get the mass operator in terms of 𝔊 and averaged single PAULI operators; the most important contributions are the RPA renormalization and the three magnon collision parts. Equations and boundary conditions of correlation functions are derived in a different manner as usually known. Detailed discussions regarding the transformation from the local into a modified spin wave representation as well as the symmetry properties of the correlation functions and their equations are given.
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