A HIGH-RESOLUTION SUSCEPTIBILITY THERMOMETER FOR USE NEAR 2 K

A relatively small and easily constructed high-resolution thermometer is described. It uses the magnetic salt copper ammonium bromide dihydr ate (CAB). Tile temperature is read out using a de-SQUID. We determine d the sensitivity of the thermometer as a function of temperature from 1.5 K to 4.3 K and for magnetic fields from 40 to 800 Gauss. Subnano- Kelvin resolution is achievable near 2 K. A mathematic model is used t o understand the measured sensitivity and to improve the design.