Weak field NMR and ESR spectrometers and magnetometers

Weak field magnetic resonance is usually limited by the signal-to-noise ratio, which decreases drastically with the field. The authors present high-resolution NMR (nuclear magnetic resonance) and ESR (electron spin resonance) sensors developed for Earth field magnetometry and spectrometry. For some of them the resonance signal is amplified by the Overhauser effect or laser optical pumping. The spectrometers and magnetometers are described. The features of magnetometers and many application fields are summarized. The performance of the low field spectrometers and their potential use in spin dynamic studies are also presented