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.

Ferromagnetic resonance (FMR) in the dependence on magnetic field orientation, and effect of the laser light on the magnetic ordering were studied in colossal magnetoresistance films, La1−xSrxMnO3 and La1−xBaxMnO3. The FMR linewidth increased with the decrease in temperature in La1−xSrxMnO3 films, and was nearly temperature independent in La1−xBaxMnO3, that was attributed to the different degree of magnetic homogeneity of the films. Layered structures La1−xBaxMnO3 on silicon with intermediate layer of SrTiO3 were characterized by FMR as highly homogeneous. From the orientation and temperature dependences of the FMR spectra, the effective magnetization, and effective anisotropy fields were estimated. The laser light illumination resulted in the change of FMR line shape and intensity, and was interpreted in terms of optically induced magnetic disordering and effective heating of the spin system.

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