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We report in detail a study of the critical dynamics of a model ferromagnet in 6-& dimensions both above and below T" for small E. The precession of spins in the local magnetic field plays a major role in the dynamics. Its effect can be ignored at 6 or more dimensions, as many authors have previously observed. At a dimension slightly less than 6, the effect is nontrivial but tractable by perturbation theory. We carry out a renormalization-group analysis and determine the dynamic exponent z = 4e/2 = 1 + d/2, accurate to O(e). We also solve the equation of motion to obtain the spin response function. The frequency and damping of spin waves below T, are determined. Forms of equations of motion and the extent of universality in critical dynamics are discussed.

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