Role of external and internal perturbations on the ferromagnetic phase transition in Sm_0.52Sr_0.48MnO₃

Abstract

We report on the magnetic field (H), hydrostatic pressure (P), and doping dependence of the order of the ferromagnetic (FM) to paramagnetic (PM) phase transition in Sm_0.52Sr_0.48MnO₃ single crystal. It has been shown that (H_cr ≈ 4 T, T_cr ≈ 160 K) is a critical point below which FM to PM phase transition is first order in nature accompanied by a sharp drop in resistivity and magnetization with thermal hysteresis. Below the critical point, these parameters also show field-induced metamagnetic transition along with hysteresis between the increasing and decreasing fields. All these signatures of first-order FM transition disappear above the critical point and the transition becomes a crossover. The effect of P on the nature of FM-PM transition is quite similar to that of H and the corresponding critical point, where the character of FM transition that changes from first to second order is (P_cr ≈ 2.5 GPa, T_cr ≈ 160 K). We have also determined the location of critical point expressed in terms of Nd concentration (y) of (Sm_1-y Nd_y) 0.52 Sr 0.48 MnO₃ and found that the transition changes to second order at (y_cr ≈ 0.4, T_cr ≈ 175 K). The change in the character of FM transition with the application of external (H and P) and internal (Nd concentration) perturbations has been explained within the framework of the formation of polarons.