Interplay Between Diamagnetic and Ferromagnetic Phase in (Bi2223)1−y(LSMO)y Composites Thick Films

Thick films of ((Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x ) 1− y (La 0.7 Sr 0.3 MnO 3 ) y [(Bi2223) 1− y (LSMO) y ] composites ( y =0.01, 0.03, 0.05) are deposited by means of a simple melting-quenching-annealing method onto (001)-oriented LaAlO 3 (LAO) substrates. The constituent compounds Bi2223 and LSMO are prepared by standard solid-state reaction and sol–gel method, respectively. Measurements of the dependence of the magnetization on the temperature show the presence of superconducting and ferromagnetic phase below ∼54 K and ∼370 K, respectively. Current–voltage measurements on composites with y =0.01, 0.03 show that the superconducting critical current drop dramatically from I c ≈350 mA at T =15 K to zero at T ≈0.5 T c (∼25 K). The dependence of the magnetization on the external magnetic field applied in-plane or out-of-plane at 5 K displays well defined hysteresis loops, which correspond to the superconducting, diamagnetic phase. For T > T c , the ferromagnetic loop of LSMO is observed. The critical current density, J c , was determined for samples with y =0.01 and 0.05 by applying Kim’s model to the superconducting, diamagnetic hysteresis recorded at 5 K. The calculated values for J c ( B ) resulted to be smaller than those obtained for individual bulk Bi2223 samples due, probably, to the presence of LSMO particles whose ferromagnetic domains compete with the superconducting diamagnetic phase.