NMR Susceptibility Measurement as an Accurate Thermometry Standard below 0.5 K

Nuclear spin systems follow the Curie law down to far below 1 mK and can provide an accurate standard of temperature below 0.5 K. Pulsed nuclear magnetic resonance (NMR) techniques are used to measure the susceptibility to an accuracy of one part in one thousand in a copper sample below 4.2 K. The method has been found experimentally to be useful down to 25 mK; the theoretical limit is much lower.