ENHANCEMENT OF T-IRR AND DELTA-M(H) IN BI2SR2CACU2OX IN THE PRESENCE OF NI PARTICLES

Magnetization measurements have been carried out as a function of temp erature and applied magnetic field, on Bi2212 particles of diameter ra nging from 62 to 88 mu m mixed with and without ferromagnetic Ni parti cles of similar diameter. The irreversibility temperature (T-irr) as w ell as the width of magnetic hysteresis loop Delta M(H) have been obse rved to increase when the Ni particles are present. Both enhancement e ffects diminish as the applied field tends to 0.5 T. These results are qualitatively understood on the basis of our new model according to w hich the Ni particles attract the vortex lines and therefore work as a n additional pinning force.