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 (400 An gstrom and 700 Angstrom) in a magnetometer at 1.5K less than or equal to T less than or equal to 300 K and in B less than or equal to 6T. On ce exposed to a magnetic-field, the sinter keeps a temperature depende nt 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 resi stance between an Ag sinter and liquid He-3. - Doped with a small amou nt of magnetic impurities, the sinter may be used as an extremely sens itive, continuously working thermometer; its susceptibility exactly fo llows the differential Brillouin function down to at least 200 mu K. T he most important advantage of this sinter is its simultaneous applica bility as thermometer and as heat exchanger in helium experiments.