A General Theory of Magnetic Resonance Absorption
Abstract
A general expression for the frequencydependent susceptibility of a magnetic system is derived by a quantumstatistical method based on the linear theory of irreversible process. This fundamental equation provides a physical ground for the socalled Fourier transform method for computing the resonance line contour. The autocorrelation function, or the relaxation function of the magnetic moment, that is the Fourier transform of the absorption intensity distribution, can be expanded in terms of the perturbation energy, which is assumed to be responsible for changes of the resonance spectrum from the unperturbed distribution. A general method is shown how to choose from the expansion terms those which contribute to a particular line of interest. This is a generalization of the method of using projection operators. The customary moment method is examined from this point of view. Introducing a further assumption, we propose a method for computing the contour of resonance lines from the obtained expansion. This may be regarded as the quantummechanical formulation of the idea employed by Anderson and Weiss for the exchange narrowing problem of paramagnetic resonance. The problem of motional effect on the broadening is treated from this general point of view. Particular applications of the theory to the motional effect of the dipolar broadening in nuclear magnetic resonance and to the exchange effect in paramagnetic cases are also discussed in detail. Some basic equations such as used by Bloembergen, Purcell and Pound for nuclear magnetic case are reexamined and corrected.
 Publication:

Journal of the Physical Society of Japan
 Pub Date:
 November 1954
 DOI:
 10.1143/JPSJ.9.888
 Bibcode:
 1954JPSJ....9..888K