Nuclear spin polarization induced solely by a rotating magnetic field

An approach to polarize the nuclei in a material, which is to apply a rotating field and induce magnetization in the direction of rotation axis, is discussed. Polarization by a rotating field was demonstrated for the case of electron spins in 1957 measurements done at Columbia University by George Whitfield and Alfred Redfield. Both the scientists measured the polarization induced by a combination of fixed and rotating field to a paramagnetic solid. The rotating field technique helps avoid complications of time dependent, inhomogeneous fields due to remnant magnetization of the rock. Lee, Hahn, and Clarke repeated their measurements of spin polarization with their liquid sample mounted on a ferrite ring, which prevented detection of proton spins prepolarized by affixed field but did not impact the measurement of proton spins polarized by a rotating field.