HE-3 MELTING PRESSURE MEASUREMENTS IN HIGH MAGNETIC-FIELDS

Experimental methods and preliminary results of high-precision measure ments of the He-3 melting curve in high magnetic fields have been desc ribed. The purpose of this work is twofold. One is to establish a reli able millikelvin temperature scale in high fields (T greater than or e qual to 10 mK, B less than or equal to 15 T). The other is to investig ate a high field region of the magnetic phase diagram of solid He-3 by measuring the melting pressure down to temperatures below 1 mK. Besid es the two superfluid transitions, the phase transition temperatures b etween the spin ordered solid and the paramagnetic solid, T-HFP, were determined at B = 12 and 10 T with good acccuracy, which is an extensi on of previous measurements up to 8 T. The present T-HFP(B) line can n ot be seabed to that at a higher density with a single Gruneisen param eter, indicating a variation of density dependencies of the multiple-s pin exchange interactions.