RF SQUID behaviour due to grain boundary weak links in a bulk YBCO is observed at 77 K using modified commercial rf electronics. Porous samples with lowIc are found to show this characteristic whereas dense samples with higherIc do not show SQUID behaviour.V-B modulation characteristic is found to be better when the rf pumping frequency is kept slightly higher than the resonance frequency of the tank circuit. Designing of coil for tank circuit with appropriateQ has been found to be very crucial for seeing the SQUID behaviour. Estimation of parameters such as coupling constant, mutual inductance, inductance and radius of the SQUID loop, have been made and their significance is discussed. Flux noise spectrum of the bulk rf SQUID in flux locked mode is also reported.
Volume 94, 2020
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