Deficiency effects on the physical properties of praseodymium-strontium manganite oxides

We investigate magnetic and magneto-transport properties in the defect Pr0. 7Sr0.3-x square (x) MnO3 (0 less than or equal tox less than or equal to0.3 ) and Pr(0.7-x)square xSr0.3MnO3 (0 less than or equal tox less than or equ al to0.23) perovskite manganite oxides. Our study is to obtain more informa tion on that different parameters that govern the magnetic and electrical p roperties in such samples. Powder X-ray diffraction patterns could be index ed in a rhombohedral perovskite structure with R $(3) over bar $e space gro up for low x values and an orthorhombic one with Pbnm space group for high x values. Lacunar compounds exhibit different behavior which depends strong ly on the vacancy type. All the praseodymium-deficient samples exhibit a pa ramagnetic-ferromagnetic transition when the temperature decreases while th e strontium-deficient ones exhibit this transition only for low x values. T he magnetic transition temperature shifts to lower values as the strontium deficiency increases (from 265 K for x=0 to 90 K for x=0.3) and to higher v alues with the praseodymium deficiency increase (from 265 K for x=0 to 315 for x=0.23). A semiconducting-metallic transition is observed for all x val ues in the praseodymium-deficient samples and only for low x values (0 less than or equal tox less than or equal to0.1) in the strontium-deficient one s when the temperature decreases. At a magnetic applied field of 2 T, Pr(0. 7)Sr(0.2)square 0.1MnO3 exhibits a magnetoresistance effect of about 65% at 150 K while for Pr(0.6)square 0.1Sr0.3MnO3, the magnetoresistance remains constant below 150 K, equal to about 20-25%. (C) 2001 Elsevier Science B.V. All rights reserved.