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Nuclear magnetic ordering in bcc 3 He has been studied by a static magnetization measurement from 10 down to 0.3 mK for a molar volume region of V = 24.14 to F = 22.46 cm 3 /mole. The results show that the ordering temperature T N varies in proportion to V 16,5 ± 1 and that the magnetization in the ordered state is constant. The magnetization reduced by its maximum value is found to be represented by a universal function of the reduced temperature T/T N . PACS numbers: 67.80.Jd, 75.30.Cr, 75.30.Kz The low-temperature properties of bcc solid 3 He have been described in terms of two-, three-, and four-particle exchange interactions. 1 These exchange interactions, which lead to nuclear ordering in solid 3 He, depend strongly on molar volume as shown by the pressure measurements at higher temperatures. 2 The spin structure in the ordered state proposed by Osheroff, Cross, and Fisher 3 suggests that the four-particle exchange process plays an important role in the antiferromagnetic ordering in solid 3 He. The magnetic properties of solid 3 He near the ordering temperature have been studied by several groups. 1 All of their results, however, have dealt with the solid for a narrow molar volume region near the melting curve. In order to investigate the molar volume dependence of the exchange interaction, we have measured the static magnetization of bcc solid 3 He through the ordering temperature for the molar volume region from 24.14 cm 3 /mole (T N = 1.01 mK) to 22.46 cm 3 /mole (r N = 0.29 mK).The experimental arrangement was almost the same as that of Prewitt and Goodkind. 4 A sample of solid 3 He was formed in the pores of a sintered silver sponge (nominal 700 A). Cooling was achieved by nuclear demagnetization of copper (22 mole). The magnetization of solid 3 He was measured statically with a SQUID magnetometer in the trapped field of 26 mT. The cell temperature was determined from the susceptibility of Pt wires by means of a pulsed NMR at a resonant frequency of 250 kHz. This NMR thermometer was calibrated against the superfluid 3 He-£ transition (Helsinki scale).A sample of solid 3 He ( 4 He less than 3 ppm) was made by a blocked-capillary method at about 2 K and annealed for one day. The molar volume of the samples was determined from the pressure in the cell with use of the data of the P-V-T relation on the melting curve. 5 For the cell pressure measurements, we made use of the system of 3 He magnetization measurements. The magnetic flux running through the pickup coil changes linearly with pressure in the cell because of the elastic expansion of the cell wall (1.5 mm thickness). No hysterisis was observed in the relation between SQUID output and the pressure up to 100 bars. With use of this measuring system, the molar volume was determined within an accuracy of ±0.02 cm 3 /mole. Although the SQUID system picks up the change of pressure as well as magnetization of solid 3 He, the two signals can be separated by the temperature region where they change predominantly. Below 10 mK, the total pressure increase du...

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