Crossover from negative to positive magnetoresistance in superconductor/ferromagnet composites thick films

Thick films of ((Bi, Pb)2Sr2Ca2Cu3Ox)0.95/(LaSr0.7Mn0.3O3)0.05 [(Bi-2223)0.95(LSMO)0.05] composites were fabricated on (0 0 1)-oriented LaAlO3 substrates by a simple melting–quenching–annealing method and their structural, morphological and magnetoelectrical properties carefully studied. Analysis of the X-ray diffraction patterns suggested a highly oriented growth along the c-axis of LSMO. This preferred orientation, with the crystal c-axis being perpendicular to the plane of the substrate, was considered to be indicative of a textured growth mode. Electrical and magnetic measurements showed the presence of ferromagnetism and superconductivity in the composite at temperatures above room temperature and below T∼50 K, respectively. A clear crossover from negative to positive magnetoresistance was observed at ∼80 K in a magnetic field as strong as 5 T.