TEMPERATURE-DEPENDENCE OF INTERACTIONS IN DILUTED MAGNETIC SEMICONDUCTORS

Coupling between the infinite and finite clusters of a spin system with the reentrant transition and spin-glass state has been studied as a function of temperature in the range from 4 K to 300 K. Thin films of CdCr2xIn2-2xSe4 with 0. 8 less-than-or-equal-to x less-than-or-equal-to 0.95 were investigated. The magnetic properties of CdCr2xIn2-2xSe4 spinel are very sensitive to the substitution of Cr by In, which leads to a random distribution of magnetic interactions. As-deposited samples had a multilayered structure of Cr/Cd-Cr-In-Se/Cr. After heat treatment we have obtained a uniform single film of controlled composition. The temperature dependence of linewidth and line shift of the ferromagnetic resonance, in parallel geometry, was used to compute the coupling parameters: M, which describes the resonance interaction between the finite and infinite clusters, and D, which is related to the relaxation processes. The models of randomly distributed spins proposed by Anderson and Continentino were applied. The model of a two-level system with asymmetric double-well potentials predicts a frequency shift due to the coupling between the infinite ferromagnetic network and finite clusters. We assume that the height of a barrier introduced in this model is a linear function of the temperature. The significant temperature dependence of coupling parameters was obtained for samples in the spin-glass state with Cr concentration x = 0.85 and 0.8. We have found that M and D are not single-valued functions of indium concentration (dilution level). We have also determined the temperature dependence of (M - D), which has an intuitive meaning as being responsible for the interaction of nondamped magnons of the infinite cluster with a two-level system. The expression (M - D) was found to be a linear function of the temperature.