Melting pressure of solidHe3through the magnetic-ordering transitions

Magnetic ordering in solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been studied by measuring the melting pressure through the various phase transitions. We find a discontinuity in entropy at the high-field–paramagnetic phase transition at low fields, indicating that it is first order. The entropy discontinuity decreases as the field increases and the transition broadens, becoming second order above a field of about 0.65 T. The first precise determination of the first-order phase boundaries has been made, from which thermodynamic data not previously available are obtained.