Colossal magnetoresistance and magnetic phase transitions in bulk $Nd0.7Ba0.3MnO3$

Perovskite-type $Nd0.7Bao0.3MnO3$ has been synthesized and its magnetic and magnetotransport properties studied in the temperature range from 5 K to 300 K. X-ray diffraction indicates that the crystal-symmetry is orthorhombic with a=0.5508(1) nm, b=0.5496(2) nm, and c=0.7764(3) nm. There exist two magnetic phase transitions. It first undergoes a paramaganetic-to-ferromagnetic phase transition at Curie temperature, $TC=115$ K, and then partial ordering of Nd magnetic moments develops at $TNd=40$ K as temperature is further decreased. Resistivity measurements indicate corresponding insulator-to-metal transition near $TC$ and a reentrant metal-to-insulator transition near 40 K. Colossal magnetoresistance exists over a wide temperature range, $MR=[R(H)-R(0)]/R(0)$ is over 90% below 120 K. The maximum MR (98%) appears at 95 K, close to the paramagnetic-to-ferromagnetic phase transition.