Comparative study of the magnetic and electrical properties of Pr 1− xBa xMnO 3− δ manganites depending on the preparation conditions

Abstract

Magnetization, electrical resistivity and magnetoresistance of Pr 0.50Ba 0.50MnO 3− δ manganites with perovskite structure have been investigated as a function of preparation conditions. It was found that the as-prepared samples (prepared in air) show T C=110 K (first order phase transition), whereas for those annealed in flowing argon the T C value increases up to 340 K without change of cubic symmetry (second order phase transition). Ferromagnet–paramagnet transition is accompanied by both a metal–insulator transition and a magnetoresistance peak. The X-ray study has revealed that the samples annealed in argon have broad peaks apparently due to microstrains and crystal structure defects. The argon-treated samples improve the magnetization after subsequent annealing in air at T⩽1000°C. T C of argon-treated samples is stable with respect to annealing in air up to 1300°C where it becomes again 110 K. In contrast, a treatment in vacuum destroys the ferromagnetic order. Auger-spectroscopy has not revealed any additional ions except Pr, Ba, Mn and O for all the samples. External pressure enhances the Curie point of the sample prepared in air at a rate of 43 K/GPa. We have observed that the samples Pr 1− x Ba x MnO 3− δ , x⩾0.30, exhibited the above-mentioned effect of increasing T C after treatment in flowing argon without changes of the phase state, whereas the samples x<0.30 decomposed into different phases. The dramatic increase of T C after argon treatment is supposed to result from microstrains and crystal structure defects in the sample.