CHARGE ORDERING AND MAGNETORESISTANCE IN ND1-XCAXMNO3 DUE TO REDUCED DOUBLE EXCHANGE

Structural, transport, and magnetic properties of Nd1-xCaxMnO3 (0 less than or equal to x less than or equal to 1) have been studied to prob e the consequence of strong lattice distortion and reduced double exch ange. Charge ordering has been observed over a large composition range of 0.30 less than or equal to x less than or equal to 0.80. For 0.33 less than or equal to x less than or equal to 0.40, at low temperature s, a magnetic field induces a first-order antiferromagnetic semiconduc tor to ferromagnetic metal transition and reduces the resistance by se veral orders of magnitude. These results illustrate the competition be tween double exchange and mechanisms that promote charge localization.