Magnetism of submicron Ag powder : its impact on the Kapitza-resistance and its applicability for thermometry at very low temperatures

We have studied the magnetic properties of submicron Ag powder (400Å and 700Å) in a magnetometer at 1.5K=T=300K and in B=6T. Once exposed to a magnetic field, the sinter keeps a temperature dependent magnetic moment whose magnitude strongly depends on the history of the sample. The dependence of the moment on the applied magnetic field is discussed in relation to the field dependence of the boundary resistance between an Ag sinter and liquid3He.-Doped with a small amount of magnetic impurities, the sinter may be used as an extremely sensitive, continuously working thermometer; its susceptibility exactly follows the differential Brillouin function down to at least 200µK. The most important advantage of this sinter is its simultaneous applicability as thermometer and as heat exchanger in helium experiments.