An electron paramagnetic resonance study of phase segregation in Nd_0.5Sr_0.5MnO₃

Abstract

We present results of an electron paramagnetic resonance (EPR) study of Nd_1-xSr_xMnO₃ with x=0.5 across the paramagnetic to ferromagnetic, insulator to metal transition at 260 K (T_c) and the antiferromagnetic, charge ordering transition (T_N=T_co) at 150 K. The results are compared with those on Nd_0.45Sr_0.55MnO₃ which undergoes a transition to a homogeneous A-type antiferromagnetic phase at T_N=230 K and on La_0.77Ca_0.23MnO₃ which undergoes a transition to coexisting ferromagnetic metallic and ferromagnetic insulating phases. For x=0.5, the EPR signals below T_c consist of two Lorentzian components attributable to the coexistence of two phases. From the analysis of the temperature dependence of the resonant fields and intensities, we conclude that in the mixed phase ferromagnetic and A-type antiferromagnetic (AFM) phases coexist. The x=0.55 compound shows a single Lorentzian throughout the temperature range. The signal persists for a few degrees below T_N. The behaviour of the A-type AFM phase is contrasted with that of the two ferromagnetic phases present in La_0.77Ca_0.23MnO₃. The comparison of behaviour of A-type AFM signal observed in both Nd_0.5Sr_0.5MnO₃ and Nd_0.45Sr_0.55Mn_O3 with the two FM phases of La_0.77Ca_0.23MnO₃, vis-a-vis the shift of resonances with respect to the paramagnetic phases and the behaviour of EPR intensity as a function of temperature conclusively prove that the Nd_0.5Sr_0.5MnO₃ undergoes phase separation into A-type AFM and FM phases.