MAGNETIC PHASE-DIAGRAM OF BCC HE-3

A complete magnetic phase diagram of bcc solid He-3 at a molar volume of 22.7 cm3/mol has been determined by pressure measurements at temperatures down to 250-mu-K in magnetic fields up to 7 T. The transition temperature between the paramagnetic phase and the high-field antiferromagnetic ordered phase increases with field and reaches a maximum (= 0.96 mK) at 3 T. Above this field, it turns to decrease and seems to be zero at 5.4 T, i.e., the upper critical field B(c2)(0). The transition is not the first-order one from 1 T to B(c2)(0). The observed reentrant phase diagram strongly supports the multiple spin exchange model, but reveals a severe quantitative inaccuracy of the mean field approximation even at high fields near B(c2)(0).