THE ORIGIN OF THE MAGNETIC CHANNEL OF THE THERMAL-BOUNDARY RESISTANCEBETWEEN LIQUID-HE-3 AND AG SINTERS AT VERY-LOW TEMPERATURES

At temperatures below about 10mK, the temperature dependence of the th ermal boundary resistance between liquid He-3 and metal sinters deviat es significantly from the behaviour expected from the acoustic mismatc h theory (R-K proportional to T-3). This behaviour is explained in ter ms of the existence of a magnetic channel for the coupling between the He-3 quasiparticles and the sinter; the origin of this coupling, howe ver, is unknown so far. In our studies of the magnetic properties of A g sinters made of powders of submicron grain size we have detected and identified a magnetically ordering subsystem which, although it contr ibutes only a few ppms to the total mass, dominates the magnetic prope rties of the sinters. We present the results of our investigation of t he magnetic properties of these Ag sinters which strongly deviate from the behaviour of bulk silver, and discuss a possible mechanism how a magnetically ordered subsystem may open up the magnetic channel of the thermal boundary resistance to liquid He-3 at very low temperatures. The main conclusion of our study is that OUT results should allow the tuning of the thermal boundary resistance between liquid He-3 and sint ered metal heat exchangers at very low, temperatures.