| Popis: |
Continuous-wave NMR was used to study the temperature dependence of the static nuclear magnetic susceptibility of solid ${\mathrm{He}}^{3}$ and solid mixtures of ${\mathrm{He}}^{4}$ in ${\mathrm{He}}^{3}$. Measurements were performed in the purest sample (3.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ ${\mathrm{He}}^{4}$ in ${\mathrm{He}}^{3}$) at four molar volumes (21, 22, 23, and 24 ${\mathrm{cm}}^{3}$/mole) in the bcc phase, and at several ${\mathrm{He}}^{4}$ concentrations ranging from 3.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ to 2.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ at 21 and 23 ${\mathrm{cm}}^{3}$/mole. The temperature range of the measurements was from 0.95 to 0.32 K. The data were fitted to a Curie-Weiss law with an rms deviation from best fit of less than ${10}^{\ensuremath{-}3}$ and best values of the Weiss constant $\ensuremath{\theta}$ were obtained. Susceptibilities and temperatures were measured to better than 0.1%. The temperature scale was based upon the susceptibility of the purest, most-dense sample. The desired accuracy in the susceptibility measurements necessitated a new method of data reduction. The accuracy in the extracted values of $\ensuremath{\theta}$ was better than \ifmmode\pm\else\textpm\fi{}1 mk. The values of $\ensuremath{\theta}$ in the purest sample (-0.24\ifmmode\pm\else\textpm\fi{}0.82 mK at 21 ${\mathrm{cm}}^{3}$/mole, -1.03\ifmmode\pm\else\textpm\fi{}1.06 mK at 22 ${\mathrm{cm}}^{3}$/mole, -1.49\ifmmode\pm\else\textpm\fi{}0.27 mK at 23 ${\mathrm{cm}}^{3}$/mole, and -3.07\ifmmode\pm\else\textpm\fi{}0.78 mK at 24 ${\mathrm{cm}}^{3}$/mole) agreed within experimental uncertainty with those of earlier workers, operating at lower temperatures. They provide a high-temperature check on those measurements. The measured effects on $\ensuremath{\theta}$ of the ${\mathrm{He}}^{4}$ impurity are consistent with the work of Richards and Homer, but the measurements show an improved accuracy. The data, as a function of $x$, the atomic fraction of ${\mathrm{He}}^{4}$, have been fitted to the equation $\ensuremath{\theta}(x)={\ensuremath{\theta}}_{0}(1+Kx)$. Values of $K$ of -430\ifmmode\pm\else\textpm\fi{}450 and -19\ifmmode\pm\else\textpm\fi{}10 were obtained at 21 and 23 ${\mathrm{cm}}^{3}$/mole, respectively. |
