To polarize the nuclei in a material, the standard approach is to apply a static magnetic field in the desired direction. A second method, recently demonstrated by experimenters at the University of California, Berkeley, is to apply a rotating field and induce magnetization in the direction of the rotation axis. 1
Nuclear polarization by a rotating field is a consequence of the phenomenological equations governing nuclear resonance written down by Felix Bloch 2 in the 1940s. The equations were modified some 10 years later 3,4 to describe cases in which a magnetic field rotating in the xy plane is comparable in magnitude to a fixed field B z. The modified equations predict—quite surprisingly—that the magnetization induced in such cases has a z-component even when the static field B z is absent.
Polarization by a rotating field was not entirely unproven. It was demonstrated for the case of electron spins in...
