Magnetic/crystalline disorder and transport phenomena inLa_(0.54)Ho_(0.11)((Sr, Ca)(K,Na))_(0.35)MnO_3manganites

摘要

La_(1-X)(Sr, Ca)~XMnO_3manganites present a special interest due their high Curie and metal-insulator transition temperatures and the possibility to obtain magnetoresistive sensors able to worknear room temperature. We have synthesized two rows of manganites, with La_(0.54)Ho_(0.11)Sr_(0.35)-_xK_xMnO)3 and La_(0.54)Ho_(0.11)Ca_(0.35-x)Na_xMnO_chemical compositions. XRD analysis, performed with aHuber diffractometer at room temperature, indicated that the manganites contain perovskite phases,with Pnma structure. The atomic positions, lattice parameters and some microstructure parameters,as average size of coherent blocks and microstrains, were obtained by using GSAS program. Thedependence of the resistivity with temperature and the applied magnetic field was determined bymeans of four probes method, between 77 and 300 K. The influence of K/Na concentration on thedisorder degree (at atomic and crystallite level) and on the transport mechanisms was discussed.