Precision magnetometry at cryogenic temperatures with gaseous 3He NMR probes.

We report on compact, gaseous 3He Nuclear Magnetic Resonance (NMR) probes for precision magnetometry of magnetic fields B > 0.1 T in the temperature range from ambient temperatures down to 4 K. The gas is polarized at thermal equilibrium under pressures up to 100 bars to provide a high nuclear spin density. To achieve sensor readout rates of O (Hz), paramagnetic substances and/or silica gel with high specific surface area were added to reduce the otherwise long T1 relaxation time of pure 3He gas and to reach thermal polarization equilibrium. Sensitivity limits, which cover the range from 10-11 < δB/B < 10-7, are accessible in a single-pulse NMR measurement and can be further improved through signal averaging in accumulated NMR scans.