HTc dc SQUID magnetometers

High sensitivity HTc dc-SQUID magnetometers, of bicrystal junction type, ha ve been designed, fabricated and characterized. The magnetometers are chara cterized by a direct-coupling planar design and their parameters and geomet rical dimensions have been optimized in order to achieve the lowest possibl e noise level. The IV characteristics are RSJ-like and show no excess curre nt. The measured SQUID normalized inductances and magnetic field modulation periods are in good agreement with the expected values. The magnetic field noise spectral densities, measured with a flux locked loop electronic setu p, exhibit typical white noise levels of about 150 fT/Hz(1/2) at frequencie s above 2KHz At lower frequencies a 1/f noise is observed. By employing a b ias-reversal electronic readout scheme, the 1/f corner frequency can be red uced to values less than 100 Hz.