EPR Studies of Rare-Earth Manganites La0.7−xEuxSr0.3MnO3 (x = 0.1–0.7)

Abstract

The Europium rare-earth manganites, La_0.7−xEu_xSr_0.3MnO₃ (x = 0.0–0.7), were investigated by the technique of X-band electron paramagnetic resonance (EPR) in the temperature range from 30 to 500 K. As the temperature was lowered, the various samples made transitions from paramagnetic to ferromagnetic phases. Furthermore, coexistence of anywhere from two to three ferromagnetic phases in the various samples was found. The third ferromagnetic phase was observed only in the samples with x = 0.1, 0.2, 0.3. The Curie temperatures for the various samples were estimated from the characteristics of the variable-temperature EPR spectra. The EPR data indicated the presence of Griffiths phases in the samples with x = 0.2, 0.3, 0.4, 0.5, 0.6, from which the respective Griffiths temperatures were determined. The activation energies were estimated here from the EPR data using the hopping model. The EPR linewidth behavior is found to be consistent with that predicted by the bottlenecked spin-relaxation model. The perovskite La_0.5Eu_0.2Sr_0.3MnO₃ is potentially useful in the design of magnetocaloric refrigeration units as a working fluid, since its Curie temperature T_C is found to be close to the room temperature. The various ferromagnetic components in the samples observed here have been resolved only by the technique of EPR, not possible by other techniques.