Magnetic fluctuations in singlet-ground-state systems
- 1 October 1976
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 14 (7), 3024-3035
- https://doi.org/10.1103/physrevb.14.3024
Abstract
This paper discusses the possible effects of coupling between different excitation modes in singlet-ground-state ferromagnets above their Curie points. The picture we use is a Hartree-like one, with every magnetic exciton dressed (in a mean-square sense) by a cloud of other such excitons. This description finds a natural expression in a functional-integral language, where the result can be expressed as a renormalization of the single-ion susceptibility by averaging over a distribution of external fields. We find that the resulting excitation spectrum has a continuum part with a threshold at the crystal-field splitting, in addition to the usual spike at the exciton frequency. The transition temperature is also significantly depressed from its random-phase-approximation value. Some numerical results are presented which suggest that these effects may be important in real systems.Keywords
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