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 0.52 Sr 0.48 MnO 3 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 MnO 3 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.