Magnetic instability in irradiated MgB2 dense samples

High density magnesium diboride samples were irradiated with low dosages of gamma-rays, protons, and electrons. They were investigated by magnetization and thermal studies in order to determine if the irradiation increases the flux pinning and consequently the critical current density Jc. Zero field cooled magnetic susceptibility and specific heat measurements confirm the bulk transition temperature (Tc) with diamagnetic signal at similar to 38.5 K. Magnetic instabilities were observed in the superconducting hysteresis loop at temperatures between 2 and 23 K in all studied polycrystalline MgB2 dense samples. The occurrence of flux jumps depended of the type of irradiation and the number of jumps decreases as temperature increases. The critical current density Jc, estimated from the magnetization hysteresis using the Bean's model, is improved for gamma irradiated sample at H=0 and T=2 K. At low temperature, the Jc decreases and several steep drops in Jc are observed as a function of applied magnetic field. Furthermore, it is observed that the influence of crystalline defects plus local disorder, induced by hot isostatic pressure and irradiation with energetic atoms, increase the Jc but at the same time the magnetothermal instabilities increase in a broad range of temperature. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3008027]