Emergence of Griffiths phase and glassy mixed phase in Sm_0.5Ca_0.5MnO₃ nanomanganites

Abstract

A detailed investigation on the effect of grain size on formation of Griffiths phase (GP), and glassy mixed phase in CE-type antiferromagnetic Sm_0.5Ca_0.5MnO₃ manganite are carried out. A rigorous measurement of linear and non-linear ac magnetic susceptibilities, time dependent relaxation and aging phenomena in Sm_0.5Ca_0.5MnO₃ nanomanganite confirm the existence of a glassy mixed phase in the low temperature regime. A strong evidence of GP has been identified in Sm_0.5Ca_0.5MnO₃ nanomanganites having ferromagnetic spin–spin correlation above Curie temperature (T_C) without possessing any spontaneous magnetization. The signature of GP in nanosized manganite has been confirmed from the detailed ac and dc magnetization studies. The existence of GP is verified through the anomalous behavior of the low field temperature dependent ac and dc magnetic susceptibility (χ) – viz., an inverse magnetic susceptibility characterized by χ^-1=(T-T_C^Rand)^1-λ with λ = 0.85 ± 0.02. Based on experimental results, the glassy phase of nanomanganites has been attributed to the phase separation effect and interaction between the ferromagnetic clusters. A phenomenological core/shell like model has also been proposed based on the surface disorder to explain the observed GP-like properties in these nanosized manganites.