COOLING OF HE-3-HE-4 DILUTE-SOLUTION DOWN TO 97 MU-K - THERMAL-BOUNDARY RESISTANCE BETWEEN DILUTE-SOLUTION AND METAL-POWDER

We have cooled a He-3-He-4 dilute solution down to 97 muK, which is th e lowest temperature ever been achieved in a dilute mixture. However, there is no sign of the superfluid transition of He-3 quasiparticles i n the solution. In the sub-millikelvin region, we have measured the th ermal boundary resistance between the solutions and sintered metal pow der as a function of temperature T We find that the thermal boundary r esistence is proportional to T-2 below 1 mK and that the resistance sh ows a strong dependence on magnetic fields below 0.1 T. These results suggest that the magnetic coupling is dominant in this temperature reg ion. We have also estimated the heat leak into the dilute solution. It is found that the heat leak is proportional to the power of one third of inverse time, and the main source of the heat leak is ascribed to the viscous movement of He-3 quasiparticles.