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Nuclear Magnetic Resonance in Solid Helium-3

1963; American Institute of Physics; Volume: 129; Issue: 2 Linguagem: Inglês

10.1103/physrev.129.630

1536-6065

H. A. Reich,

Advanced NMR Techniques and Applications

Nuclear magnetic resonance experiments have been performed in solid ${\mathrm{He}}^{3}$ at constant molar volumes in the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ phases at various magnetic fields and temperatures by the spin-echo method. The self-diffusion coefficient $D$ as well as the relaxation times ${T}_{1}$ and ${T}_{2}$ have been determined. $D$ is observed to obey the Arrhenius equation as the temperature is lowered in the $\ensuremath{\alpha}$ phase, but at a low enough temperature it becomes temperature independent and depends only on the density. The activation energy for diffusion correlates well with that determined from specific heat measurements. At high magnetic fields ${T}_{1}$ and ${T}_{2}$ are observed to obey the Bloembergen, Purcell, and Pound relationships characteristic of relaxation caused by diffusion. At low magnetic fields, ${T}_{1}$ becomes temperature independent as the temperature is lowered, and is observed to depend on magnetic field as $\mathrm{exp}(\frac{{H}^{2}}{H_{0}^{}{}_{}{}^{2}})$, implying that the relaxation is from Zeeman to exchange systems. Values of the exchange integral $J$ are deduced from temperature-independent diffusion, field-dependent relaxation, and rigid-lattice values of ${T}_{2}$, and show fair agreement internally. No agreement can be obtained with values of $J$ deduced from observations of departures from Curie's law, the values here reported being much smaller.