EPR concentration dependence in magnetically diluted crystals with strong spin-spin interaction

Abstract

Experimental investigations of electron paramagnetic resonance have been made in ionic crystals using diamagnetic samples with paramagnetic impurities and also in solid solutions in a large range of concentration. There exist cases in which neither the moment nor the statistical method could until now give even a qualitative explanation of the EPR linewidth and amplitude concentration dependence experimentally observed. In particular, this is true for the MnOMgO solid solutions observed in the concentration range 10 - ̊ 3 to 0.8. It is believed that it is necessary to take into account spin-spin interactions (although not very small interactions) and magnetic clusters. A numerical statistical method, making no use of perturbation theory with respect to the interaction, is presented for considering multiparticle spin-spin interactions. A universal computer program using the ALGOL-60 language has been elaborated and applied, and the results for MnOMgO solid-solution polycrystalline powders are given. Despite ambiguity concerning the literature data on the exchange constants and the small number of neighbors used ( n = 5), the nonmonotonic character of the experimental curves giving the linewidth and amplitude concentration dependence may be qualitatively explained by the influence of the dipolar and exchange interactions.