Ferromagnetism in the lacunar (Pr, Sr)MnO 3 perovskite manganites

Abstract

Structural, magnetic and magneto-transport properties in the defect Pr 0.7− x □ x Sr 0.3MnO 3 (0⩽ x⩽0.23) and Pr 0.7Sr 0.3− x □ x MnO 3 (0⩽ x⩽0.3) perovskite manganite oxides have been investigated. Our samples have been elaborated by the conventional ceramic method. Structural analysis shows that all samples have a perovskite structure with different distortion degrees. X-ray diffraction patterns show that our samples are in a single phase. Strontium-deficient samples crystallized in a rhombohedral structure with R 3 ̄ c space group for 0⩽ x⩽0.2 and in the orthorhombic symmetry with Pbnm space group for x>0.2; while in the praseodymium-deficient samples, the rhombohedral to orthorhombic transition occurs for x>0.1. All the praseodymium-deficient samples exhibit a paramagnetic–ferromagnetic transition when the temperature decreases while the strontium-deficient ones exhibit such transition only for low x values. The magnetic transition temperature shifts to lower values as the strontium deficiency increases and to higher values with the praseodymium-deficient increase. With decreasing temperature, all the praseodymium-deficient samples exhibit a semiconducting-metallic transition, while such transition is observed only for low x values (0⩽ x⩽0.1) in the strontium-deficient ones. At a magnetic applied field of 2 T, stoichiometric sample Pr 0.7Sr 0.3MnO 3 exhibits a magnetoresistance (MR) effect of about 60% at 265 K. For the strontium-deficient samples ( x=0.05 and x=0.1), the MR at a magnetic applied field of 2 T is found to be about 90% for Pr 0.7Sr 0.25□ 0.05MnO 3 and 70% for Pr 0.7Sr 0.2□ 0.1MnO 3. For the praseodymium-deficient sample ( x=0.1), the MR remains constant below T ρ =250 K at a value of about 20–25% for H=2 T.