Dynamic orientation of a deuteron-spin system by rf irradiation of a polarized-proton-spin system

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Abstract
We have observed a high degree of orientation of a deuteron-spin system in partially deuterated organic materials. This was obtained by dynamic polarization, using a 25-kG magnetic field and a dilution refrigerator, followed by slightly off-resonance rf irradiation of the polarized-proton-spin system, which causes a cooling of the proton spin-spin interaction reservoir. Thermal contact between this reservoir and the one made up of the deuteron quadrupole interactions provides a simultaneous cooling of the latter reservoir, which corresponds to a change in the deuteron tensor polarization or alignment. Alignment values around 60% were observed for some parts of the inhomogeneous deuteron-spin system, which corresponds to a spin termperature for the quadrupole reservoir of 7 μK. The dependence of the alignment on radio frequency and initial proton polarization as well as the thermal mixing rates are in good agreement with quantitative estimates from the spin-temperature theory.