Operation of high-temperature superconductor magnetometer with submicrometer bicrystal junctions

We investigated the noise properties of dc superconducting quantum interference device flip-chip magnetometers with submicrometer-wide bicrystal junctions operating at 77.4 K. The noise of the magnetometers with electronics was about 6 fT/√Hz at frequencies above 100 Hz increasing up to about 20 fT/√Hz at 1 Hz. The operation of the magnetometers was characterized in an electronic axial first order gradiometer system, which was employed for biomagnetic measurements. The system demonstrated a gradient resolution of about 1 fT/cm√Hz at 77.4 K and stable operation in a standard magnetically shielded room under clinical conditions.