Inverse colossal magnetoresistance and NMR study in lacunar perovskite manganites Pr0.7Sr0.2□0.1MnO3 and Pr0.6□0.1Sr0.3MnO3

Both Pr 0.7 Sr 0.2 □ 0.1 MnO 3 and Pr 0.6 □ 0.1 Sr 0.3 MnO 3 ceramic samples have been studied by several techniques including 55 Mn nuclear magnetic resonance, magnetic, resistivity and magnetoresistance measurements. Powder X-ray diffraction patterns do not exhibit secondary phases in significant amount. Both samples crystallize in the rhombohedral perovskite structure with R3c space group. They exhibit a paramagnetic (PM)-ferromagnetic (FM) transition at 160 and 290 K for Pr 0.7 Sr 0.2 □ 0.1 MnO 3 (sample I) and Pr 0.6 □ 0.1 Sr 0.3 MnO 3 (sample II), respectively, while the PM-FM transition in the stoichiometric sample Pr 0.7 Sr 0.3 MnO 3 occurs at 265 K. The PM-FM transition in sample I is followed by a magnetization decrease with decreasing temperature indicating a spin canted state at low temperature. Resistivity measurements as a function of temperature show a semiconducting-metallic transition at Tp = 250 K for sample II and a semiconducting-metallic transition at 160K followed by a resistivity increase with decreasing temperature for sample I. Both samples exhibit a magnetoresistance at 2 T in the vicinity of the semiconducting-metallic transition temperature Tp of about 65% and 20% for samples I and II, respectively. Furthermore, we observe for sample I an inversion of the CMR from negative at high temperature, to positive CMR at very low temperatures (T