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Cross-polarization of nuclei (I) with a low magnetogyric ratio is one of the pillars of many modern solid state NMR experiments, enhancing the sensitivity often by an order of magnitude. Cross-polarization is based upon cross-relaxation in the rotating frame between different nuclides, and occurs when the Hartmann-Hahn condition (2) is met. For magnetization transfer from spin Z to spin S, this condition requires radiofrequency fields, HI and Hs, applied simultaneously close to resonance for spin Z and spin S, respectively. H, and Hs must have the relation r&Jr = rsfk 111 where yr and ys are the respective magnetogyric ratios. If spin Z is abundant, the minimum rf field strength, HI, required for cross-polarization is dictated by the fact that HI must be strong enough to generate a spin-lock of spins, Z, and is thus determined by the strength of the homonuclear Z-Z spin interaction (3, 4). In practice, a HI value on the order of 10 G is often needed for protons. This means that if one wants to cross polarize, for example, 15N nuclei, a 15N rf field strength on the order of 100 G is needed. For lower-y nuclei, even higher rf field strength