Step-Edge High-${\rm T}_{\rm c}$ SQUID Magnetometer for Low-Field NMR Detection

The fabrication processes for step-edge high- T
_c
superconducting-quantum-interference-device (SQUID) magnetometers have been developed. A magnetometer consists of three SQUIDs, which can be activated either individually or in series. Thus, the transfer function can be manipulated by activating a single SQUID or multiple SQUIDs in series. Furthermore, such a SQUID magnetometer is benefited by that if one of the three SQUIDs is broken, the other two SQUIDs are still workable. In addition to characterizing the SQUID magnetometer, the application of the SQUID magnetometer in the low-field nuclear magnetic resonance (NMR) has also been investigated. The results has shown a clear NMR signal of 4230 Hz for the water under 99.3 μT.