Temperature Dependence of the Upper Critical Field in bcc Solid 3He

The temperature dependence of the upper critical field for the antiferromagnetic high-field phase of bcc solid ³He has been calculated by Iwahashi and Masuda utilizing the Green-function method with Tyablikov decoupling. In the low temperature limit the upper critical field, H _c2(T), is found to decrease from H _c2(0) with increasing temperature as a power law with exponent 3/2. Interestingly, the same power law dependence has been predicted for a system of dilute magnons undergoing Bose–Einstein condensation and has been observed in the spin-gap antiferromagnets TlCuCl₃, BaCuSi₂O₆, and NiCl₂–4SC(NH₂)₂. An experiment has been attempted to determine precisely the temperature dependence of the upper critical field in bcc solid ³He by measuring the pressure of the solid during adiabatic demagnetization through the critical field. The theoretical framework motivating the experimental study is presented along with details of the experimental setup.