ESR spectra of trimeric heteronuclear clusters. I. Theory

A theory of the ESR spectra of trimeric heteronuclear clusters consisting of transition-metal ions has been developed. The theoretical model includes both isotropic exchange and Dzialoshinskii-Moriya antisymmetric interactions; it also takes into account the differences between g values of the individual ions. The energy levels of the interacting multielectronic ion system in a magnetic field have been found in theory. Radiofrequency transition probabilities have been determined for the canonical directions of the field. It is shown that the ESR spectrum exhibits peculiarities closely related to the non-linear behaviour of Zeeman levels.