Nuclear Spin System of LiquidHe3

The entropy and heat capacity of spin disorder in liquid ${\mathrm{He}}^3$, obtained previously, define the partial thermodynamic potentials of the spin system. These in turn lead to the spin equation of state. The energy of spin excitation, quadratic in the liquid temperature at low temperatures, tends toward the limiting value of $\frac{1}{2}k{T}_0$, per spin, at high temperatures, $T_0$ being the empirical characteristic temperature of the spin system. The partial volume expansion coefficient of liquid ${\mathrm{He}}^3$, arising from the spin excitations, is a linear function of the temperature at low temperatures and of considerable magnitude, which might make it accessible experimentally. The effect of the spin excitations on the vapor pressure of liquid ${\mathrm{He}}^3$ might also be separable through a careful analysis of the data over a wide temperature interval.