Effect of oxygen content on magnetization and magnetoresistance propertiesof CMR manganites

The influence of oxygen content on the magnetization and electrical resisti vity of Ln(0.5)A(0.5)MnO(3) (Ln=La, Pr, Nd; A=Ca, Ba) manganites with the p erovskite structure is investigated. It is shown that the La0.5Ca0.5MnO3-ga mma compound undergoes a sequence of transitions from an antiferromagnetic (gamma =0) to a spin-glass (gamma =0.17) state and then to an inhomogeneous ferromagnetic (gamma =0.3) state. A transition from an antiferromagnetic c harge-ordered state to a ferromagnetic charge-disordered state in Nd0.5Ca0. 5MnO3-gamma is observed as the oxygen content is reduced to where gamma =0. 07. The Nd0.5Ba0.5MnO3-gamma compound shows an increase of the Curie point from 110 K(gamma =0) to 310 K(gamma =0.3). In addition, a large magnetoresi stance is revealed which develops below their Curie temperature despite the absence of Mn3+-Mn4+ pairs. A Zener double-exchange interaction is usually used in literature to explain the magnetic and electrical properties of ho le-doped perovskite manganites. The data obtained support the mechanism of superexchange interactions between magnetic moments of the manganese ions v ia oxygen. (C) 2001 American Institute of Physics.