Direct detection of low-frequency NMR using a dc SQUID

Abstract

A system has been developed to directly observe NMR free induction signals at very low frequencies. We use a nonresonant pickup arrangement with a commercial dc SQUID to monitor the precessing magnetization in a 0.5–50-kHz range of Larmor frequencies. A relocking interval for the SQUID’s flux locked loop presently sets our pulse recovery around 20–30 μs throughout this frequency range. The noise for this system is less than 1.5 times that recorded for the SQUID with shorted input terminals.