Observation of Griffith-like phase at room temperature in La0.9Sr0.1MnO3 nano-particles
Y. S. Chen (陳友生)1*, K. L. Liang (梁凱玲)1, C. C. Chang (張嘉倩)1, J. G. Lin (林昭吟)1
1Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
* presenting author:陳友生, email:youshengchen@ntu.edu.tw
La1-xSrxMnO3 half-doped manganites attract high attentions due to the colossal magnetoresistance (CMR) effect1 related to Griffiths singularity2 which yields a critical percolation threshhold (~0.08) for a ferromagnetic (FM) insulating homogeneous phase of La0.9Sr0.1MnO3 (TC ~ 150 K). On the other hand, Griffith phase which contains both FM and paramagnetic (PM) domains could be induced by intrinsic inhomogeneity at a transition temperature TG (275K) above TC.2 Such Griffith phase is also affected by the size of manganites when the sample dimension is downscaled to nano meter. Previous studies indicate many interesting phenomena related to size effects including the size-induced structural transition, core-shell phase separation and the enhancement of magnetization and exchange bias. However, studies on nano-size effects are mostly focused on the doping of FM metallic phase. Recently, room temperature ferromagnetism is reported in nano-sized insulating La0.9Sr0.1MnO3,3 which remains to be understood. In this work, temperature dependent magnetization (M-T) and electron spin resonance (ESR) are investigated in La0.9Sr0.1MnO3 nano-particles. ESR is a very sensitive way to detect the core-shell phase separation and FM signal in Griffith phase as seen from Figure 1. The field dependent M-T results show the coexistence of two magnetic phases which is similar to Griffith phase in bulk or manganites. However, ESR experiment reveals the absence or low contribution of PM phase and the existence of second magnetic phase which are highly different from bulk samples. Our results indicate the core-shell structure could be the cause of the anomaly in Griffith phase for La0.9Sr0.1MnO3 nano-particles.

Keywords: LSMO, nanoparticle, electron spin resonance