Sangeeta Chaudhry

RF SQUID behaviour in YBCO thick films up to 85 K

RF SQUID behaviour has been observed in screen-printed thick film of YBCO up to 85 K. A hole shunted with a microbridge type of geometry has been made manually on the film. Phase reversal in V- Phi behaviour, which is a characteristic feature of the RF SQUID, is also observed at 77 K. The flux noise spectrum has been found to depend sensitively on the quality of the film. Films containing 123 phase as well as 211 phase show more 1/f noise than films containing only 123 phase.

Performance of Bi-Sr-Ca-Cu-O thick film rf SQUIDs at liquid nitrogen temperatures

Periodic oscillations in the V‐Φ characteristics have been observed up to 97 K in radio frequency SQUIDs fabricated from screen printed Bi‐Sr‐Ca‐Cu‐O thick films. The SQUID has been operated successfully in the flux‐locked‐loop mode at 77 K. Stability of the SQUID output and its noise performance have been found to improve considerably when the SQUID is operated in the flux‐locked‐loop mode as compared to that in the open‐loop mode. The spectral noise density, in the white noise region, is 5×10−4 Φ0/√Hz at 77 K for the flux‐locked‐loop mode.

Behaviour of thick film BiSrCaCuO rf SQUID at 77 K

Abstract Rf SQUID effect has been observed in BiSrCaCuO thick film at 77 K. The films were prepared using screen printing technique on MgO (100) substrate with the starting composition of 1112. The superconducting film has Tc(R=0) ∼ 100 K. A hole shunted with a microbridge is carved manually for observing rf SQUID effect. Flux noise spectrum of the SQUID has been studied at 77 K. The flux noise in this device is relatively less than that observed in thick film YBaCuO rf SQUID.

Growth kinetics of high Tc phase in Bi-Sr-Ca-Cu-O thick films

Thick films of Bi–Sr–Ca–Cu–O on (100) MgO substrates have been prepared by the screen printing technique with the starting composition of 1112. The annealing process involves a two-step heat treatment. The first-step temperature is chosen between 874 °C and 898 °C for 45 min followed by slow cooling (2 °C/min) to 864 °C. In the second step, the films are kept at 864 °C for a time varying from 0 to 104 h. The T c ( R = 0) and intensity of the characteristic peaks of the high T c and the low T c phases in the x-ray diffraction pattern are found to be dependent on the first-step temperature and the duration of the second step. The process of crystallization and the growth of plate-like grains as a function of annealing time at the second step are studied using Scanning Electron Microscopy (SEM). Kinetics of the growth of the high T c phase has been explained in terms of a reaction mechanism involving the first and second annealing steps.

Observation of RF SQUID behaviour in BSCCO thick film upto 96 K

Abstract RF SQUID behaviour in superconducting thick films of BSCCO has been observed upto 96 K. A geometry of a single hole shunted with a microbridge is carved manually on the film for observing the rf SQUID behaviour. Phase reversal in V-Φ patterns with increasing rf current, which represent a typical feature of a rf SQUID, is clearly observed. Flux noise spectrum of the SQUID is also studied.

Superconducting thick films of Bi2Sr2CaCu2O8+x with zero resistivity at 96 K

Thick screen-printed films of Bi2Sr2CaCu2O8+x on (100) MgO substrate have been prepared with zero resistivity at 96 K. The processing technique involves two-step heat treatment at 880 degrees C and 864 degrees C followed with a rapid quenching to ambient temperature. The X-ray diffraction studies reveal formation of single-phase oriented films of composition 2212. The enhancement of Tc has been attributed to the favourable oxygenation of the usual 85 K phase.

Performance of YBaCuO thick film rf SQUIDs at 77 K

RF SQUID behaviour has been observed at 77 K in YBaCuO thick films prepared by screen printing technique. A hole shunted with a microbridge type of geometry is patterned manually for observing rf SQUID behaviour. Flux noise spectrum is also studied and it is found to depend on the quality of the film. The spectral density of the flux noise in the white noise region is 1.7×10−3 Φ0/√Hz at 77 K.

Detection of small magnetic fields using thick BSCCO film RF squid operating at 77 K

Abstract A high T c RF SQUID fabricated from thick BSCCO film using naturally present grain boundary weak links has been used for measuring small magnetic fields originating from an analogue quartz wrist watch and magnetic rock samples. For these measurements, the samples were kept at ambient temperature at a distance of ≈4 cm from the SQUID, which was operated in the ‘locked mode’ at 77 K. The flux noise density of the SQUID in the white noise region was 5 × 10 −4 Φ 0 Hz − 1 2 at 77 K.

Growth of highT c Bi-Sr-Ca-Cu-O thick films

Thick films of Bi-Sr-Ca-Cu-O were deposited on (100) MgO substrates by screen-printing technique with the starting composition 1112. To attain the superconducting state, the films were subjected to two-step heat-treatment. R-T and XRD have been studied for films annealed at different durations of the second step. InitiallyTc (R=0) increased from 77 to 103 K as the annealing duration was increased after whichTc decreased. Kinetics of the growth of highTc phase is discussed in the light of our results.

Annealing effects on growth of high Tc, phase in BiSrCaCuO screen printed film

Annealing effects of two step heat treatment have been studied on BiSrCaCuO films made by screen printing. The volume fraction of high Tc phase is sensitive to the temperature of first step. The method has proved effective in obtaining large volume fraction of high Tc phase.