Magnetic-field-induced insulator-metal phenomena in perovskite manganese oxides

Phenomena of colossal magnetoresistance (MR) or magnetic-field-induced insulator-metal (I-M) transitions have been investigated for single crystals of perovskite-type manganese oxides with controlled carrier density and one-electron bandwidth. In addition to the canonical MR behaviors near the Curie temperature. the first-order phase transition accompanying a several orders of magnitude change in resistivity has been observed under an external magnetic field for many of the composition-controlled crystals as an intrinsic bulk phenomenon. It was proved by the systematic experimental investigations that the collapse of the charge-ordered state under a magnetic field, which accompanies the lattice-structural as well as metamagnetic transition, is a major origin of such a colossal MR. Versatile MR phenomena and I-M phase diagrams in the T-H plane are presented with their interpretations.