A-site deficiency effects on the structure, magnetic and transport properties of Pr0.6−x□xSr0.4MnO3 (0 ≤ x ≤ 0.2) perovskite manganite

Praseodymium-deficient Pr0.6−x□xSr0.4MnO3 (x = 0, 0.05, 0.1, 0.15 and 0.2) polycrystalline samples have been studied by X-ray diffraction, magnetic and transport measurements. Our samples have been synthesized by the solid state reaction method at high temperature. Structural characterization showed that all our samples crystallize in the orthorhombic system with Pbnm space group. Praseodymium deficiency leads to a decrease of the unit cell volume. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our samples are ferromagnetic at low temperature. With increasing praseodymium-deficient amount, the Curie temperature TC shifts from 310 K for x = 0 to 254 K for x = 0.2. All our samples exhibit a semiconducting-metallic transition with decreasing temperature. The maximum of the resistivity increases and the semiconductor–metallic transition temperature TMI decreases as the deficiency content increases. In the ferromagnetic metallic region (T < TMI), the resistivity of the samples are well fitted using the expression ρ=ρ0+ρ2T2+ρ9/2T9/2ρ=ρ0+ρ2T2+ρ9/2T9/2 implying the importance of scattering process. In the high temperature regime, the resistivity data can be well described by the small polaron model. The polaron binding energy varies from 192 to 202 meV with increasing deficient amount. Under a magnetic applied field, a significant reduction in the resistivity and a shift of TMI to higher values are observed. With increasing temperature, the magnetoresistance ratio for Pr0.4□0.2Sr0.4MnO3 sample remains constant up to 200 K and then decreases, it is found to be about 15% at 300 K.