Calorimetry of bcc SolidHe3through the Nuclear Magnetic Ordering Temperature in a Magnetic Field

The nuclear magnetic specific heat of bcc solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ of molar volume 24.15 ${\mathrm{cm}}^3$/mole has been measured as a function of temperature $T$ and magnetic field $B$ for $0.6 \mathrm{mK} <T<\mathrm{}40\mathrm{} \mathrm{mK}$ and $B<\mathrm{}8.0\mathrm{}$ T. The discontinuous change in entropy following the high-field to low-field phase transition has been also measured. The magnetic phase diagram has been determined. The observed specific-heat peak at the ordering temperature $T_N$ is discussed in connection with the nature of the phase transition.