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 ofLaGa1−xMnxO3, in a broad range of the Mn ion concentration, . With increase in Mn concentration, a complex multi-line spectrum, typical for low Mnconcentrations, evolves to an exchange-narrowed several- or single-line spectrum atx>0.05. The temperature behaviour of the ESR line-width in the range of 80–300 K is found to bevery different in the materials with high and intermediate concentration of Mn ions: a slight growth of the line-width isobserved in the former case, while a steep line narrowing occurs atx = 0.05 and 0.1 with increase in temperature. Similar temperature dependence of the line-width isalso observed for an additional ESR line arising in the non-stoichiometric oxygen-deficientLaMnO3−δ manganite. We explain the experimental data by taking into account the effect of thethermo-activated Jahn–Teller reorientation process on spin dynamics in Mn clusters, andestimate its activation energy as 50–100 meV.