Abstract
The co-existence of colossal positive and negative magnetoresistance has been observed in a perovskite-type material Nd0.67Ca0.33MnO3. The hysteretic behavior of resistivity in temperature and magnetic field suggests the existence of phase transition. Positive magnetoresistance (positive-MR = [rho(B) - rho(0)]/rho(0)) up to 10000% was observed below insulator-metal transition temperature, TI-M similar to 45 K, accompanied by a negative magnetoresistance (negative-MR) with further increasing magnetic field. The positive-MR may be attributed to the field-induced carrier localization (CL). whereas the wry large negative-MR is believed to be due to the field-induced collapse of charge ordering.