Superconductive quantum interference magnetometer with high sensitivity achieved by an induced resonance.

A fully integrated low noise superconducting quantum interference device (SQUID) in a magnetometer configuration is presented. An intrinsic high voltage responsivity as high as 500 muV/Phi0 has been obtained by introducing a resonance in the voltage - magnetic flux characteristic. This resonance is induced by an integrated superconducting coil surrounding the pick-up coil and connected to one end of the SQUID output. The SQUID magnetometer exhibits a spectral density of magnetic field noise as low as 3 fT/Hz(1/2). In order to verify the suitability of the magnetometer, measurements of bandwidth and slew rate have been performed and compared with those of the same device without the resonance and with additional positive feedback. Due to their good characteristics such devices can be employed in a large number of applications including biomagnetism.