EVIDENCE FOR AN ENHANCED MAGNETORESISTANCE ACCOMPANYING A CONTINUOUS-PHASE TRANSITION IN SEMICONDUCTING LA0.67MG0.33MNO3

The field-and temperature-dependent ac susceptibility of Mg-substitute d LaMnO3 provides unequivocal evidence for the presence of critical fl uctuations associated with a continuous paramagnetic-to-ferromagnetic transition at which all three static critical exponents are estimated independently. Furthermore, this system does not undergo a metal-insul ator transition near T-c, exhibiting a monotonic increase in resistivi ty with decreasing temperature in available fields. Nevertheless, this system displays a near colossal magnetoresistance that peaks near T-c , indicating a probable magnetic origin for this effect but of rather different character from that found in other perovskites.