Magnetic field dependent critical current density of Bi-Sr-Ca-Cu-O superconductor in bulk and tape form with addition of Fe3O4 magnetic nanoparticles

The (Bi, Pb)(2)Sr2Ca2Cu3O10-(Fe3O4)(x) superconductor for x = 0, 0.01, 0.03, and 0.05 were prepared. The average size of Fe3O4 used was 40 nm. The maximum critical current density (J(c)) in the bulk form was observed in the x = 0.01 sample. Based on this result, Ag sheathed high temperature superconductor tapes with starting compositions (Bi, Pb)(2)Sr2Ca2Cu3O10-(Fe3O4)(0.01) were fabricated using the powder in tube method. The microstructure, phase formation, critical temperature, and transport critical current density were studied. The J(c) of the nanosized Fe3O4 added tapes is 5130 A/cm(2) at 77 K and 23130 A/cm(2) at 30 K in zero fields. The nonadded tapes showed a lower J(c), 3090 A/cm(2) at 77 K and 12 400 A/cm(2) at 30 K. A sudden decrease in J(c) in low magnetic fields (B < 0.10 T) when applied parallel and perpendicular to the tapes surface was observed. By adding magnetic nanoparticles, the full vortex magnetic energy can be used to enhance J(c) and thus, magnetic nanoparticles such as Fe3O4 can act as an effective flux pinning center leading to the enhancement of J(c) in the bulk as well as the tape form. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3070628]