Low-temperature grain boundaries effect in La0.7−Y Ca0.3MnO3

The influence of the Y doping on the magnetic properties of La 0.7− x Y x Ca 0.3 MnO 3 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, susceptibility and magnetisation measurements. The evolution of the magnetic state with yttrium doping is first described and then correlated with the low-temperature magnetoresistance effects. Y doping does not influence in a monotonic way the coercive field or the initial susceptibility of the samples, but modifies the magnetic state from a ferromagnetic ( x =0) to a cluster glass ( 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.