Thermal and magnetic properties of liquid <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:math> at low pressure and at very low temperatures (1965)

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.A careful discussion is given of the techniques developed for obtaining and maintaining temperature below $\mathit{0.010}\ifmmode^\circ\else\textdegree\fi{}K$ for many hours in an apparatus of moderate size using superconducting magnets. Details are given of the method of using epoxy resins for producing apparatus for using ${He}^{3}$ with application to the measurement of heat capacity and magnetic properties. The method of executing the experiments is presented together with a thermodynamic analysis of the effectiveness of the final cooling process.New measurements of the heat capacity of a mixture of low pressure ${He}^{3}$ and CMN are presented down to a magnetic temperature of $\mathit{0.004}\ifmmode^\circ\else\textdegree\fi{}K$. No anomalous results are obtained. The experimental technique is analyzed and criticized. The results are compared with earlier data. The limiting value of $C/nRT$ still cannot be precisely assessed but seems to be in the range $\mathit{3.0}$ to $\mathit{3.2}\ifmmode^\circ\else\textdegree\fi{}{K}^{\ensuremath{-}1}$. Detailed comparison is made of the present work with that of Peshkov, whose results are interpreted in terms of an experimental effect. The thermal boundary resistance from epoxy walls to ${He}^{3}$ compares favorably with previous work.Measurements by the spin-echo method of the self-diffusion coefficient, $D$, and the susceptibility, $\mathrm{Χ}$, of the ${He}^{3}$ are presented down to a temperature of $\mathit{0.0035}\ifmmode^\circ\else\textdegree\fi{}K$ No anomalous behavior is observed. $D$ obeys the law $D=\mathit{1.36}\ifmmode\times\else\texttimes\fi{}{\mathit{10}}^{\ensuremath{-}6}{T}^{*\ensuremath{-}2}{cm}^{2}{K}^{\ifmmode^\circ\else\textdegree\fi{}2}{sec}^{\ensuremath{-}1}$. to below $\mathit{0.005}\ifmmode^\circ\else\textdegree\fi{}K$. If an experimental effect is corrected for, $\mathrm{Χ}$ appears to be temperature independent. Assuming that $D$ defines the Kelvin temperature by $T\ensuremath{\propto}{D}^{\ensuremath{-}\textonehalf{}}$, the present work measures $\mathrm{Χ}$ vs $T$ without recourse to an auxiliary thermometer. The same assumption leads to the conclusion that the Kelvin and magnetic temperatures differ by only $\mathit{0.0001}\ifmmode^\circ\else\textdegree\fi{}K$ at $\mathit{0.0035}\ifmmode^\circ\else\textdegree\fi{}K$. The ${He}^{3}$ spin-lattice relaxation time, measured down to $\mathit{0.004}\ifmmode^\circ\else\textdegree\fi{}K$ where it is about 2 sec in the present cell, decreases with decreasing $T$ but without a well defined temperature dependence.