COLOSSAL MAGNETORESISTANCE IN THE ANTIFERROMAGNETIC LA0.5CA0.5MNO3 SYSTEM

We have explored the colossal magnetoresistance (CMR) effect in the an tiferromagnetic 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 tr ansition, and correspondingly, an insulator to metal transition. The o bserved CMR is attributed to the H-induced charge localization-delocal ization behavior associated with the AFM-FM transition. At low tempera tures (T<100 K), the solid remains in the AFM phase, where we have obs erved a phenomenal one millionfold change in resistivity between 0 and 8 Tesla. The origin of CMR in low T-region is a thermal activation en ergy gap which is strongly dependent on H. (C) 1996 American Institute of Physics.