A Magnetic Temperature Scale from 1 to 83 K

The low frequency (30 Hz) paramagnetic susceptibilities of powdered samples of gadolinium sulphate octahydrate and manganous ammonium sulphate hexahydrate have been measured from 1 to 83 K in order to test the thermodynamic consistency of the International Practical Temperature Scale of 1968 (IPTS-68). The data can be characterized by a physically based expression with essentially two constants as opposed to the twenty-one terms of the IPTS-68 Reference Function for the range 13.81 K to 273.15 K. Variations in the IPTS-68 of up to ± 3 mK about the smooth magnetic scale are found and the 20.28 K (e-H 2 b.p.) fixed point is shown to be inconsistent with the other fixed points by about +3 mK. The data also provide a means of thermodynamically extrapolating the IPTS-68 to lower temperatures where comparisons are made with other recent data. The reproducibility of the data is ± 0.5 mK below 50 K and ± 1 mK up to 83 K, while the total estimated measurement uncertainties are from one to three times greater.