Magnetic Resonance for Nonrotating Fields

A treatment of the magnetic resonance is given for a particle with spin ½ in a constant field H0 and under the action of an arbitrary alternating field with circular frequency ω perpendicular to H0. A method of finding a solution, valid at any time, is given which converges the better the smaller the deviations from a rotating field or the larger H0. It is shown that in the lowest order correction the shape of the resonance curve is unchanged but that it is shifted by a percentage amount H12/16 H02 where H1 is the effective amplitude of the oscillating field. This also involves a correction in the values of the magnetic moments thus obtained towards smaller values which however in all practical cases is negligibly small.