Magnetic Coupling betweenHe3andF19at Low Temperatures

Measurements of relaxation phenomena between liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ nuclei in small fluorocarbon particles are reported. Magnetic cross relaxation between the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ in the substrate and the liquid is observed in measurements between 1 K and 0.6 mK. The spin temperatures remain strongly coupled in magnetic fields up to 125 mT. Moreover it is observed that there is a decrease in magnetic relaxation time at the onset of superfluidity in the liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and that the thermal relaxation times are remarkably short at all temperatures.