Abstract
Ac magnetic-flux penetration in a disk-type sample of sintered Bi2Sr2CaCu2Ox high-Tc superconductors was examined under a relatively low magnetic field excitation of 10 kHz at 72 K, using a planar coil. The results indicated some interesting non-linear magnetic-flux-penetration phenomena. Increases and decreases of the ac excitation field yielded a hysteresis ac magnetic-flux penetration characteristic. The onset of flux penetration took place at a certain value of ac excitation, and thereafter the penetration developed strongly with slight increases in excitation until it reached a stable state. The superposition of a dc bias field on the ac excitation field enhanced the ac magnetic-flux penetration. Once the ac magnetic flux penetration was completed by the dc bias field, the ac magnetic-flux penetration was sustained, even though the dc bias field was decreased to zero, presenting evidence of a dc magnetic-flux remanence. The remanence disappeared in about 10 s after both the ac excitation and the dc bias field were cut off.
