Evidence of emerging Griffiths singularity in La0.5 Sr0.5 MnO3 nanocrystalline probed by magnetization and electron paramagnetic resonance

We present an investigation of Griffiths singularity in La0.5 Sr0.5 MnO3 nanocrystalline by means of magnetic susceptibility and electron paramagnetic resonance (EPR). An unusual platform was found in paramagnetic region. Based on the analysis of EPR spectrum and magnetization variation across the whole temperature range of phase transition, we confirm it is due to the presence of Griffiths singularity rather than a superparamagnetic state in the nanocrystalline system. Such a singularity phase is constituted with some correlated ferromagnetic clusters which embed in paramagnetic matrix. Although they form ferromagnetic spin correlation, the system do not yield any spontaneous magnetization. According to core-shell model, the emergence of Griffiths singularity can be considered due to the presence of local ferromagnetic fluctuations originated from surface spin disorder as the sample size is confined to nanoscale.