New, high-performance, hydrogenated paramagnetic solution for use in earth field DNP-NMR magnetometers

The low-field nuclear magnetic resonance signals of solvent protons, enhanced by dynamic polarization, have been measured using a new paramagnetic solution of 1,1,3,3-tetramethylisoindol-N-oxyl (TMIO) free radical in triethylene glycol dimethyl ether(triglyme). The signal characteristics are compared with those of our previous standard solution for Earth field magnetometers, Enhancement factors varying between 1000 and 2000 are obtained between 25 and 125 degrees C; these results, which are the best ever obtained for stable radicals over such a large temperature range, are interpreted in the framework of relaxation matrix formalism with the help of extensive EPR line width measurements. In addition, this system is very efficient in high magnetic field gradients, owing to the relatively short NMR relaxation times T-2.