Magnetic field induced properties of manganite perovskites with colossal magnetoresistance (invited)

We present a systematic study of the magnetotransport and magnetic properties of the half-doped La(0.5)Ca(0.5)MnO(3+delta)system. The solid is a metamagnet which undergoes a first-order antiferromagnet (AFM) to ferromagnet (FM) phase transition under a field or by changing temperature. Associated with the AFM-FM transition is an insulator to metal transition. A maximum 10(9)-fold magnetoresistance ratio has been observed at 4.2 K between the least and the most conductive states. At low T (less than or equal to 50 K), we have also observed two additional metastable electronic states in the canted AFM state at certain fields. The resistivity of each state differs from one another by at least one order of magnitude. The existence of these multiple states may be related to the unique charge- and spin-ordered state of the half-doped manganite. (C) 1997 American Institute of Physics.