INFLUENCE OF CHARGE AND MAGNETIC-ORDERING ON THE INSULATOR-METAL TRANSITION IN PR1-XCAXMNO3

A detailed study of the properties of Pr1-xCaxMnO3 shows that for a ra nge of compositions (0.3 less than or equal to x<0.5) there is a first -order magnetic-field-induced insulator-metal transition. For the x= 0 .4 composition the magnetic and charge ordering (CO) effects are decou pled with antiferromagnetic (AFM) ordering, T-N=170 K, developing at c onsiderably lower temperatures than the CO state, T-CO=250 K. Below th e CO temperature, metamagnetic transitions exist that transform the ma gnetic correlations from either paramagnetic or AFM to ferromagnetic. Metastable conducting states are formed below 25 K.