THEORY OF RF MOSSBAUER-SPECTRA OF THE MAGNETICS WITH MAGNETIC-ANISOTROPY

The theory of the r. f. collapse phenomenon in nuclear γ resonance (NGR) for magnetics is proposed. In contrast to the existing rotating‐field and stepwise‐field models this approach takes into consideration the detailed behaviour of the magnetization (consequently of hyperfine field (HF) under external r. f. field and magnetic anisotropy field. Using the Liouville superopetor technique the expression for NGR absorption cross‐section (57Fe) is obtained on the basis of time periodicity of the HF alone. The possibility of the chaotic evolution of the magnetization in some cases and the corresponding changes in the NGR spectra are shown. Numerical model calculations for a system of single domain particles with uniaxial anisotropy using the chain fraction method are carried out. So the matter under discussion is a quantitative to the r. f. collapse regime valid for an arbitrary time dependence of the HF. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA