Nuclear Paramagnetism of Helium-3—Helium-4 Solutions above 0.9°K

Abstract

The temperature dependence of the nuclear susceptibility of pure ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{3}$-${\mathrm{He}}^{4}$ mixtures of ${\mathrm{He}}^{3}$ concentrations 0.81, 0.70, 0.38, and 0.14 has been determined with an accuracy of \ifmmode\pm\else\textpm\fi{}1% for $0.92<T<2.9$\ifmmode^\circ\else\textdegree\fi{}K. This work is an extension of that of Fairbank, Ard, and Walters, and shows that within experimental error the temperature dependence for the solutions is the same as that of the pure liquid. The maximum deviation of the susceptibilities from an inverse temperature dependence is approximately 5%. These results indicate that the susceptibility is insensitive to the average separation of the ${\mathrm{He}}^{3}$ atoms, contrary to the behavior that might be expected from a Fermi system in which exchange is important. A perturbation calculation, however, suggests that such behavior can be understood as a near cancellation of terms arising from the exclusion principle and the exchange interaction.