Measurements of Demagnetizing Factors and Their Application to Magnetic Thermometry

Shape corrections for several cerous magnesium nitrate magnetic thermometers have been measured, both for powders and for composites of oriented single crystals, in an attempt to establish a suitable geometry for a magnetic thermometer accurate to ∼1% at temperatures down to 0.02°K. The results indicate that this accuracy is available with either a spherical composite of oriented single crystals. or with a powder in the form of a right circular cylinder with ratio (length/diameter)=0.92. In either case it is imperative that the density be uniform within the sample. The results are compared with theoretical computations, where applicable, and with the results of other techniques.