Pinning stability and the introduction of pinning centers are essential problems in the application of high temperature superconductors. A study of the role of the addition of a variety of oxides into Gd-123 bulk superconductors was pursued with respect to the effect of magnetic pinning centers on enhancement of critical current density. We have found the addition of magnetic alloy particles into Gd-123 bulk contributes to the enhancement of the critical current density under a magnetic field. The magnetic particles of Fe-B alloy with small amounts of Cu-Nb-Si-Cr were added into the Gd123 matrix and grown into single-domain bulk in air. The effects of Fe-B alloy magnetic particles on the superconducting pinning properties of Gd123 bulk are reported. The experimental results showed that the Tc of the bulk was suppressed significantly and the transition width became larger with an increase in the doping content of the magnetic particles. This was consistent with magnetic impurities suppressing superconductivity. The critical current density deduced from the magnetization as a function of applied external magnetic field was enhanced under low magnetic field and high magnetic field, which is different from the bulk doped with paramagnetic particles. Possible mechanisms and the role of magnetic materials from the viewpoint of increased flux pinning inside the bulk are discussed.
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