A tuned NMR spectrometer using a DC SQUID for systems of low spin density

Abstract We are using a low T c DC SQUID as the first-stage amplifier in an NMR spectrometer designed for the study of systems of low spin density. The NMR pickup coil forms part of a series tuned tank circuit attached to the input coil of the SQUID. The tank circuit resonant frequency is close to 1 MHz. The SQUID amplifier uses additional positive feedback (APF) and operates in flux-locked loop mode with a bandwidth of 1.6 MHz. Preliminary measurements on 3 He samples are reported.