A study of the magnetoresistance effect in Bi-2212 for the purposes of utilisation in magnetic field sensors

The magnetoresistive (MR) effect in Bi-2212 was studied through the creation of a number of Bi-2212 composites for the purposes of utilization as the active component in a magnetic field sensor. Bi-2212/USr2CaO6, Bi-2212/MgO, Bi-2212/CeO2 and Bi-2212/Ag composites were made with varying concentrations of impurities. The MR effects of these composites were characterized and compared to that of pure Bi-2212 and that of the other composites. The resistivity of the Bi-2212 composites with the exception of the Bi-2212/CeO2 and Bi-2212/Ag can be characterized by a high sensitivity to applied magnetic field over an increasing temperature range with increasing impurities concentrations up to a percolative limit. Bi-2212/CeO2 composites display a highly insulating behavior indicative of a breached percolative limit while the Bi-2212/Ag composite displays a decreased resistance as the Ag improves conductivity with the HTS. X-ray results show the compatibility of the added impurities with the stability of the Bi-2212 matrix in all cases except CeO2 addition during the melt texturing (MT) process. Bi-2212/USr2CaO6 and Bi-2212/MgO showed the most potential for cryogenic magnetic field sensing applications, and so Bi-2212 + 6.6wt% USr2CaO6 MT composite and Bi-2212 + 20wt% MgO MT composite were tested at 77K and cycling fields of 0-1T. They showed high sensitivity to applied magnetic fields and no hysteresis. Bi-2212 + 20wt% MgO MT composite bulk proved to be the most promising composite for the purposes of cryogenic magnetic field sensing, and so a prototype cryogenic sensor was built with Bi-2212 + 20wt% MT composite bulk as the active component.