Colossal magnetoresistance in the antiferromagnetic La_0.5Ca_0.5MnO₃ system

We have explored the colossal magnetoresistance (CMR) effect in the antiferromagnetic La0.5Ca0.5MnO3 compound. In the absence of a magnetic field (H), the solid is a canted antiferromagnetic (AFM) insulator. An applied H in the Tesla scale induces a first order AFM to FM phase transition, and correspondingly, an insulator to metal transition. The observed CMR is attributed to the H-induced charge localization-delocalization behavior associated with the AFM-FM transition. At low temperatures (7<100 K), the solid remains in the AFM phase, where we have observed a phenomenal one millionfold change in resistivity between 0 and 8 Tesla. The origin of CMR in low T-region is a thermal activation energy gap which is strongly dependent on H. © 1996 American Institute of Physics.