Magnetic and electrical properties of the lacunar La_(0.7)Ca_(0.3-x)□_xMnO_3 and La_(0.7-x)□_xCa_(0.3)MnO_3 oxides

摘要

Previous studies on lacunar Ln_(0.7-x)A_(0.3)MnO_3 and Ln_(0.7)A_(0.3-x)MnO_3 with Ln = Pr, Nd and A = Sr, Ba perov-skite manganese oxides have shown that their magnetic and electrical properties depend strongly on the nature of the deficient-element. In order to confirm such behaviour, we investigate the effects of lanthanum and calcium deficient upon the physical properties of La_(0.7)Ca_(0.3)MnO_3 oxide. La_(0.7)Ca_(0.3-x)□_xMnO_3 and La_(0.7-x)□_xCa_(0.3)MnO_3 powder samples have been elaborated by the conventional ceramic method at 1400 K. All our synthesized samples are single phase and exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. With increasing vacancy content, the Curie temperature decreases in the calcium-deficient samples and increases in the lanthanum-deficient ones. With increasing x from 0 to 0.2, T_C is found to decrease from 218 to 180 K in the first series and to increase from 218 to 248 K in the second one. Resistivity measurements versus temperature showed that all lanthanum-deficient samples exhibit a semiconducting-metallic transition with decreasing temperature, however, such transition has been observed only for low x values (x ≤ 0.1) in the calcium-deficient samples.