Magnetism of Solid Helium-3

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9421034 Adams Several problems in nuclear magnetism of solid helium-3 will be investigated at temperatures as low as 20 microkelvin and magnetic fields up to 20 Tesla. Ordering in the high-pressure hexagonal-closed packed phase, which is expected to be ferromagnetic because of the dominance of triple exchange, will be achieved by using the helium nuclei for the second stage demagnetization. The high field to paramagnetic phase transition, which occurs near 20 Tesla where the system becomes fully magnetized, will be studied by measurement of the melting pressure to obtain the magnetization. The nature of this transition at low fields near the triple point ( where the low-field, high-field, and paramagnetic phases coexist) will be investigated by nuclear magnetic resonance and thermal transport measurements. These three investigations will provide additional insight into the fundamental behavior of this model magnetic substance. %%% Solid helium-3 is considered a model magnetic system for studying fundamentals of magnetism. Because of the small mass and weak forces between atoms, the effect of interest occur in a range of temperature near absolute zero, below that of interest for electronic systems, but above those for heavy nuclear magnets. Since the helium is highly compressible, effects can be investigated over a wide range of density by application of moderate pressure. In particular, the type of magnetic structures occurring in two different type of crystals can be studied. Methods of investigation include nuclear magnetic resonance, melting pressure, constant-volume pressure, and thermal conductivity. Knowledge gained will be of use in understanding magnetic phenomena in more complicated magnetic systems. ***