COLOSSAL MAGNETORESISTANCE OF FERROMAGNETIC MANGANITES - STRUCTURAL TUNING AND MECHANISMS

The amplitude Delta rho(T,H)/rho and temperature T-M, where the coloss al magnetoresistance (CMR) response of L(1-x)Ca(x)MnO(3) manganites ar e maximum, are found to be controlled by the radius of the lanthanide (L(3+)) which modifies the bending of the Mn-O-Mn bond. Increasing the bond distortion lowers T-M and enhances Delta rho(T,H)/rho. Enhanced CMR arises from (1) a shift to lon er temperatures of T-M, (2) a reduc ed mobility of the doping holes, and (3) an increase of the coupling b etween itinerant and localized electrons. The resistivity rho(H) follo ws an approximate to BM(2)(H) law and the parameter B is also tuned by the Mn-O-Mn bond angle. The narrowing of the electronic bandwidth is the fundamental parameter controlling the observed CMR.