Observation of NMR Signals from a Thin 3He Slab

NMR free precession signals from a slab of normal 3 He of thickness comparable to the superfluid coherence length have been observed using a SQUID NMR spectrometer at a frequency of 880 kHz. This spectrometer is based on a SQUID with Additional Positive Feedback, directly coupled to a low noise room temperature amplifier, and operated in flux locked loop mode using the direct offset integration technique, with a bandwidth of several MHz. The sensitivity is such that the signal from a 100 nm slab on a 1 cm 2 surface, corresponding to 2 * 10^ 17 spins, is clearly resolved.