OPERATION OF HIGH-TEMPERATURE RF SQUID MAGNETOMETERS USING DIELECTRIC SRTIO3 RESONATORS

The operation of YBa2Cu3O7 rf superconducting quantum interference devices (SQUIDs) using a dielectric SrTiO3 resonator as tank circuit was tested. At 77 K, we attained for such resonators unloaded quality factors Q(0) up to 7000 at resonant; frequencies near 1 GHz, when measuring without electromagnetic shielding. For a washer SQUID with an area of 4x4 mm(2) and an inductance of similar or equal to 100 pH, which was properly coupled to the resonator, we measured an approximately 60 mu V peak-to-peak SQUID signal and a white flux noise spectral density of S-phi(1/2) = 1 x 10(-5)Phi(0)/root Hz, corresponding to a field sensitivity of B-N=105 fFT/root Hz. With an additional single-layer flux transformer with a diameter of the pickup loop of 22 mm in flip-chip arrangement,the field sensitivity was improved to 30 fT/root Hz. (C) 1995 American Institute of Physics.