Magnesium, a promising dopant for the improvement of the CMR properties of perovskite manganites

The study of the substitution of magnesium for manganese in the type I Pr-0.7(Ca,Sr)(0.3)MnO3 and type II Pr0.5Sr0.5MnO3 manganites has been performed. Remarkable colossal magneto resistance (CMR) properties have been evidenced for the manganites Pr0.7Ca0.2Sr0.1 Mn1-xMgxO3, with x less than or equal to 0.02, for which R(OT)/R(7T) resistance ratio values ranging from 10(4) to 4.10(5) at 105 K and 70 K respectively were obtained in a magnetic field of 7 T. The study of the type II phases Pr(0.5)Sr(0.5)M(1-x)Mg(x)O(3), shows their similarity with the trivalent metal doped manganites Pr(0.5)Mn(1-x)M(x)O(3) with M = Al, Ga, In, in contrast to the tetravalent metal doped manganites with M = Ti, Sn. The latter properties are interpreted in terms of two factors, the molar ratio Mn(III): Mn(IV), and the size of the doping cation.