MAGNETIC-FIELD-INDUCED METAL-INSULATOR-TRANSITION IN PEROVSKITE-TYPE MANGANESE OXIDES

The competition between ferromagnetic metallic state due to double exc hange and antiferromagnetic nonmetallic state due to an ordering of Mn 3+/Mn4+ with 1/1 (charge ordering) has been studied with use of single crystals of perovskite-type manganese oxides prepared by the floating zone method. The charge-ordered state can be altered to a ferromagnet ic metallic state by application of a magnetic field, which accompanie s a change in resistivity by several orders of magnitude. This is one of the major origin of the colossal magnetoresistance (CMR) in these m anganese oxides.