Thermal and magnetic properties of liquid He3 at low pressure and at very low temperatures

Abstract

A brief review of the experimental and theoretical properties of low pressure liquid ${He}^3$ as related to the present work is given. This is followed by a discussion of the magnetic cooling method as applied to cooling ${He}^3$ using both nuclear and electronic paramagnetics. A number of possible metals for nuclear cooling are suggested, while cerium magnesium nitrate (CMN) is taken to be the best electronic paramagnetic known for the present purposes. The spin-bath thermal resistance is discussed in both cases. In the case of CMN recent work on the spin-bath resistance, due to a phonon bottleneck, shows it to be remarkably low. This is borne out in the present experiments. It is concluded that for temperatures in the millidegree range CMN is the best possibility.