A new concept for integrated YBa/sub 2/Cu/sub 3/O/sub 7/ magnetometers

We present an integrated magnetometer concept that combines inductance matching by a flux transformer with the low inductance of a multiloop pick-up coil. Using ramp-type Josephson junctions with PrBa/sub 2/Cu/sub 3/O/sub 7/ barriers, a 90 pH dc SQUID together with a five turn flux transformer is coupled to a multiloop pick-up coil. The dependence of the effective area of the magnetometer on the temperature is investigated by successively disconnecting the pick-up loops. The 1/f flux noise of the integrated magnetometer is suppressed by operation in a flux-locked loop mode with bias current modulation. This results in a flux density noise of /spl radic/(S/sub B/)(1 Hz,77 K)=100 fT//spl radic/(Hz). Using this magnetometer, different biomagnetic measurements have been performed.