Low-temperature grain boundaries effect in La0.7-xYxCa0.3MnO3

The influence of the Y doping on the magnetic properties of La0.7-xYxCa0.3 MnO3 compounds (x = 0; 0.07; 0.1; 0.15) and on the low-field and high-field magnetoresistance responses are investigated by means of transport, suscep tibility and magnetisation measurements. The evolution of the magnetic stat e with yttrium doping is first described and then correlated with the low-t emperature magnetoresistance effects. Y doping does not influence in a mono tonic way the coercive field or the initial susceptibility of the samples, but modifies the magnetic state from a ferromagnetic (x = 0) to a cluster g lass (x = 0.15), The key observation is that by relatively low temperatures (50 K) the resistivity change in low magnetic fields is controlled by the bulk magnetisation value only, independent of the Y content. It is further shown that the high-field behaviour of resistivity depends on the increased spin disorder resulting directly from the presence of yttrium. (C) 2000 El sevier Science B.V. All rights reserved.