Cobaltites: New materials with magnetoresistance properties

Oxygen-deficient perovskite cobaltites Sr1−xAxCoO3−δ and SrCo1−yMyO3−δ′ have been prepared by solid-state reaction. These compounds can be either ferromagnetic metals or magnetically disordered insulators. Magnetoresistance values in 7 T reach −5% near TC and up to −17% at 5 K. These properties are discussed in the light of the eg character of the conduction band revealed by Seebeck measurements.