Nuclear Magnetic Susceptibility of Solid He3 and of Dilute Solid Mixtures of He4 in He3

Abstract

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×${10}^{-5\mathrm{}}$ ${\mathrm{He}}^4$ 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×${10}^{-5\mathrm{}}$ to 2.0×${10}^{-2\mathrm{}}$ 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 ${10}^{-3\mathrm{}}$ and best values of the Weiss constant $\theta$ 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 $\theta$ was better than ±1 mk. The values of $\theta$ in the purest sample (-0.24±0.82 mK at 21 ${\mathrm{cm}}^3$/mole, -1.03±1.06 mK at 22 ${\mathrm{cm}}^3$/mole, -1.49±0.27 mK at 23 ${\mathrm{cm}}^3$/mole, and -3.07±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 $\theta$ 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 $\theta \mathrm{}\left(x\right)={\theta }_0\mathrm{}(1+Kx)\mathrm{}$. Values of $K$ of -430±450 and -19±10 were obtained at 21 and 23 ${\mathrm{cm}}^3$/mole, respectively.