GIANT MAGNETORESISTANCE IN BULK SAMPLES OF LAMNO3 WITH VARYING MN4+ CONTENT

Magnetoresistance (MR) in bulk samples of LaMnO3 has been investigated by varying the Mn4+ content from 10 to 33 per cent by chemical means, without aliovalent doping. With the increase in Mn4+ content, the str ucture of LaMnO3 changes first from orthorhombic to rhombohedral and t hen to cubic and the material becomes increasingly ferromagnetic, exhi biting a resistivity maximum akin to an insulator-metal transition at T-Peak, just below the ferromagnetic T-c. The magnitude of MR is highe st in the cubic sample (with 33% Mn4+) around the T-Peak, and negligib le in the non-magnetic orthorhombic sample (12% Mn4+).