Magnetic Phase Transitions in bcc 3He

We study magnetic phase transitions in the bcc solid ³He by means of Monte Carlo simulations. We employ a classical spin model on the bcc lattice with multiple ring-exchange interactions. In the present study, we take into account up to 4-spin ring exchanges. In order to clarify the character of phase transitions we examine energy histograms generated by Monte Carlo simulations. It is shown that the phase transition between the cnaf and the paramagnetic phases is discontinuous at low magnetic fields while it is continuous at high magnetic fields. This result agrees qualitatively with experimental observations.