Rf-SQUID effect in Hg(Tl)-Ba-Ca-Cu-O high-Tc thin film up to 121 K

Hg(Tl)-Ba-Ca-Cu-O high-Tc films have been prepared by the spray pyrolysis technique. The process involves preparation of a precursor film of Ba-Ca-Cu-O followed by annealing in a Hg-Tl atmosphere. The resultant film had Tc approx. 127.5 K and predominantly consisted of 1223 phase. An rf-SQUID has been fabricated using natural grain boundary weak links. The SQUID shows good voltage-flux modulations at 77 K and the peak-to-peak voltage of the modulation remains constant up to 118.5 K. It starts decreasing above 118.5 K and finally disappears at 122 K. The flux noise density of the SQUID at 2 Hz and 77 K is 2x10-3Φ0 Hz-1/2. It does not change much up to 117.4 K and shows a peak at 120.5 K. (author)