Effect of diamagnetic dilution and non-stoichiometry on ESR spectra in manganites

Abstract

ESR spectra are studied in a series of diamagnetically diluted manganites,single crystals of LaGa 1−x Mn x O 3 , in a broad range of the Mn ion concentration, 0 < x 1. With increase in Mn concentration, a complex multi-line spectrum, typical for low Mn concentrations, evolves to an exchange-narrowed several-or single-line spectrum at x > 0.05. The temperature behaviour of the ESR linewidth in the range of 80-300 K is found to be very different in the materials with high (x 0.2) and intermediate (0.05 x 0.1) concentration of Mn ions: a slight growth of the line-width is observed in the former case, while a steep line narrowing occurs at x = 0.05 and 0.1 with increase in temperature. Similar temperature dependence of the line-width is also observed for an additional ESR line arising in the non-stoichiometric oxygen-deficient LaMnO 3−δ manganite. We explain the experimental data by taking into account the effect of the thermoactivated Jahn-Teller reorientation process on spin dynamics in Mn clusters, and estimate its activation energy as 50-100 meV.

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