Large magnetoresistance in antiferromagnetic CaMnO3-δ

CaMnO3-delta with delta = 0, 0.06, and 0.11 was prepared by the Pechini citrate gel process at 1100 degrees C. Oxygen defects were created by quenching the sample from high temperature. Chemical analysis and x-ray absorption show that the formal valence of Mn in CaMnO3 is close to 4+, and that Mn(III) is created in the quenched samples. Moreover the x-ray absorption near-edge spectra results support the creation of two Mn(III) five coordinate sites fur each O vacancy. CaMnO3-delta (delta = 0- 0.11) are n-type semiconductors and order antiferromagnatically with Neel temperatures close to 125 K. The activation energy decreases with increasing delta. A relatively large (similar to 40%) negative magnetoresistance (MR) is observed for CaMnO2.89. This result shows that a substantial MR can occur in these G-type antiferromagnetic materials. [S0163-1829(99)02913-6].