The critical behavior at the paramagnetic to ferromagnetic phase transition in ${\text{Pr}}_{0.5}{\text{Sr}}_{0.5}{\text{MnO}}_3$ is studied using techniques such as modified Arrott plot, Kouvel-Fisher plot, and critical isotherm analysis. Though the nature of this transition is found to be of second order, the estimated critical exponents $\beta$, $\gamma$, and $\delta$ are in between the theoretically predicted values for three-dimensional Heisenberg and mean-field interaction models. However, it is noteworthy that the scaling relations are obeyed indicating renormalization of interactions around the Curie temperature $\left(T_C\right)$. Temperature variation in effective exponents (${\beta }_{\text{eff}}$ and ${\gamma }_{\text{eff}}$) resemble with those for disordered ferromagnet. It is shown that fully localized-spin interaction models are not applicable for this compound, and ferromagnetic interaction has itinerant character. Moreover, the exponents determined in this study are close to those calculated from the results of renormalization group approach for a heuristic model of two-dimensional Heisenberg spins coupled with long-range interaction. These results suggest that critical phenomenon in ${\text{Pr}}_{0.5}{\text{Sr}}_{0.5}{\text{MnO}}_3$, which is found to be an inhomogeneous ferromagnet around $T_C$, could not be described within the framework of existing universality classes and probably belong to a separate class.

• Received 7 April 2009

DOI:https://doi.org/10.1103/PhysRevB.79.214426