Nuclear susceptibility of solid 3He

Nuclear susceptibility of solid 3He along the melting curve has been measured from 12 mK down to the ordering temperature. Susceptibility measurements were made by a pulsed NMR method at frequency of 227.5 kHz. As the decay time constant is limited by the field inhomogeneity, the integrated values are considered to be proportional to the magnetization of 3He. The experimental cell is illustrated, in which a fine copper wire (diameter 15 μm, length 190 m) is packed in the space surrounded by the NMR coil. During the measurements, the temperature in the cell is controlled by feeding back off-balance signal of the capacitance bridge to the 4He pressurized system. Compressional cooling is started from 23 mK. When the cell is cooled down to the measuring temperature region, about 25% of the volume inside the NMR coil is already filled with solid 3He. Application of heat into the cell through the copper wire results in increase of magnetization signal as more solid is formed around the wire. The observed thermal relaxation time does not exceed several minutes even at lowest temperature. The authors' data extended to 1 mK clearly show the deviation from the Curie-Weiss relation below 5 mK, in accordance with the tendency suggested in previous papers. This feature may help the understanding of the discrepancy between the observed ordering temperature and that deduced from higher temperature data. (Wakatsuki, Y