Magneto-transport and thermal properties of Pr2/3Ba1/3(Mn1−xSbx)O3 system

Abstract

Magneto-transport and thermal studies on Sb-doped Pr2/3Ba1/3(Mn1−xSbx)O3 (0 ⩽ x ⩽ 0.03) manganites are reported here. Two transitions (at TP1 and TP2) observed in the electrical resistivity behaviour of pristine sample Pr2/3Ba1/3MnO3 shift to lower temperatures with an overall increase in the electrical resistivity. Electrical resistivity upturn observed at low temperatures gets enhanced with increasing Sb content and the minimum resistivity temperature shifts to higher temperatures. Intrinsic magneto-resistance (MR) at TP1 gets suppressed whereas extrinsic MR gets enhanced with Sb-doping. With higher Sb content two MR peaks are observed and MR at the low temperature peak is higher than at the high temperature peak. Thermoelectric power (TEP) of the pristine sample shows a transition from an insulating behaviour at high temperatures to a metallic behaviour at low temperatures. With Sb-doping TEP shows anomalous behaviour as a peak is developed near the phase transition (TP1) due to the weakening of the double-exchange mechanism and increase in magnetic inhomogeneity of the samples. Conduction at high temperatures is due to the hopping of small polarons and the activation energy increases due to the localization of carriers with Sb-doping. Electron–magnon interaction in the metallic region also gets suppressed with Sb-doping. Specific heat measurements exhibit a peak below TP1 and the area under the peak decreases, indicating the increase in magnetic inhomogeneity with Sb-doping. Thermal conductivity κ above TP1 is a result of the local anharmonic distortions associated with small polarons. The anomalous peak in κ around TP1 is attributed to a competition of the reduction in the Jahn–Teller distortion and magnon–phonon scattering enhancement.