Standardization of Critical Temperature Measurement by Magnetic Method

Magnetic critical temperature of composite superconductors has been studied for providing a new standard method for the critical temperature measurement. Various magnetization-temperature curves of Cu/NbTi, Cu/Nb3Sn and Ag/Bi-2223 wires were measured using a SQUID magnetometer and an ac susceptometer. In the case of SQUID magnetometer measurements, we employed a two-field-direction method to obtain higher resolution near the onset temperature. In ac susceptometer measurements, various amplitudes from 2 Oe to 10 Oe with frequencies from 11.3 Hz to 1033 Hz were applied to three specimens to study the suitable ac magnetic field and frequency range. Analytical comparison of the magnetic curves with the resistive curves was also accomplished to investigate the validity of the new method as compared with the existing one.