Transport and magnetic properties in perovskite compound La0.7Sr0.3Mn1-xCoxOy

Magnetic and transport properties of the series La0.7Sr0.3Mn1-xCoxOy (x = 0, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1.0) have been investigated. It was found that with increasing Co content, the Curie temperature TC decreases, while the spin glass transition temperature Tg decreases first then increases. As for the sample with x = 0.3, the relation of Tg and the merging point Tm (for the zero-field-cooled and field-cooled magnetization curves starting to merge) with the applied magnetic field H follows a relation Tj/TC = 1-αHβ(Tj = Tm, Tg), where α and β are constants. The resistivity increases drastically with Co doping and a semiconductor-like behaviour is displayed in the sample x = 0.3. These facts strongly suggest that the double-exchange interaction in the perovskite materials is very fragile since a small Co content can change the magnetic and relevant transport properties of the system. (author)