Electron Spin Resonance Study on Room-Temperature Ferromagnetic La0.9Sr0.1MnO3 Nanoparticles

Temperature-dependent electron spin resonance (ESR) is applied to investigate La_0.9Sr_0.1MnO₃ nanoparticles incorporating with magnetization and electrical transport measurements. Ferromagnetism is observed at room temperature which is much higher than the T_C value for bulk samples (~150 K). The ESR analysis confirms the coexistence of multiple magnetic phases consistent with the field-dependent magnetization-temperature curves. By fitting ESR spectra, the room-temperature multiphases are identified as the mixture of ferromagnetic and paramagnetic states, similar to the Griffiths phase observed in bulk samples. The field-dependent resistivity shows colossal magnetoresistance effect up to room temperature. Based on our analysis, the size-effect-induced room-temperature ferromagnetism is strongly correlated with the enhancement of the Griffith phase separation temperature.