Effects of impurities addition in MgB2/Nb tapes on flux jumps instability and critical current density

In order to understand the effect of impurities inclusions on the transport properties of MgB2 tapes, by means of magnetization measurements we have analysed non-commercial monofilamentary tapes in which titanium (Ti), tungsten (W) and silicon carbide (SiC) normal particles were included. All the samples under analysis have the same cross section and their MgB2 filament is embedded in a superconducting niobium matrix. For all the tapes a magnetic field (Ha) up to 65 kOe has been applied parallel to the filament, and we have compared their magnetization loops M(Ha) measured in the temperature range from 2 K up to 30 K. The results show that the process of adding normal particles in the material, in order to increase the transport properties, produces at low field opposite effects to those at higher field. Moreover, all the particles included produce the common result of an enhancement in the thermomagnetic instability, and consequently a decrease of the transport properties, at low temperature and magnetic fields.