Theory of Ferro- and Antiferromagnetic Resonance in Solids Containing Ions of Complicated Level Structure

The time-dependent molecular-field (TDMF) approach to magnetic resonance is described and illustrated with six examples. For the simplest models, the random-phase approximation of TDMF is equivalent to Tyablikov spin waves. However, whereas Green's function and spin-wave techniques are forced into same-site decorrelation approximations when confronted with complicated single-ion dynamics, TDMF is general enough to include any single-ion terms without difficulty. Ions appear as coupled oscillators whose allowed transitions are pulled in forming collective modes. The procedure, being quite general, is readily automated and is thus convenient in actual calculations for physical problems.