Concentration dependence of the macroscopic magnetic anisotropy and of the ferrimagnetic line width in the gallium substituted europium iron garnet

Abstract

Available experimental results on the dependence on concentration of the ferrimagnetic resonance of gallium substituted europium iron garnet, have been used to study the dependence on concentration of the macroscopic anisotropy constant K1 and the ferrimagnetic line width ΔH. Instead of employing a strict molecular field theory, the probabilities of finding different numbers of Fe ions that are first and third nearest neighbors to each Eu have been used to derive ΔH and K1. This method is an extension of the statistical treatment introduced by Nowik and Ofer to study the Mossbauer spectra of the same substituted garnets. The statistical theory gives a better description of the dependence of K1 on concentration than does a strict molecular field theory. Although the results obtained seem to indicate that the spin-lattice relaxation of Eu in EuIG is independent of the exchange field HH that measures the Fe–Eu interaction, these results do not seem conclusive enough to reject a relaxation rate proportional to H2ex.