Derivation of matrix elements for the system of moment equations governingthe kinetics of superparamagnetic particles

An exact equation for the matrix elements of the system of moments [the exp ectation values of the spherical harmonics (Y-l,Y-m)(t)], which govern the kinetics of the magnetization M of single-domain particles is derived. This derivation is based on the representation of the stochastic Gilbert equati on augmented by a random field and the corresponding Fokker-Planck equation for the distribution function of the orientations of M in terms of the ang ular momentum operators and the subsequent evaluation of the matrix element s in terms of the Clebsch-Gordan coefficients. (C) 2000 Elsevier Science B. V. All rights reserved.