Integrated dc SQUID magnetometer with a high slew rate

We have fabricated a magnetometer in which the thin-film superconducting pick-up loop and dc SQUID are integrated on a single silicon chip. The magnetometer, which is intended primarily for geophysical applications, has a magnetic field sensitivity of typically 5×10−15 T Hz−1/2 at frequencies above about 10 Hz, and 2×10−14/( f /1 Hz)1/2 T Hz−1/2 at lower frequencies. The dynamic range is ±2×107 Hz1/2 and the maximum slew rate is about 4×10−3 T s−1 at 6 kHz. This high slew rate enables the magnetometer to be operated in a flux-locked loop for long periods of time without losing lock.