ZERO WAVE VECTOR KINETIC COEFFICIENT IN THE ISOTROPIC FERROMAGNET EUO NEAR TC

We have measured the zero wave vector kinetic coefficient and relaxation time for the isotropic Heisenberg ferromagnet EuO using zero-field electron spin reasonance. Measurements were made by monitoring the absorptive part of the uniform susceptibility χ (q=0,ω;T) at fixed frequency, ω/2π?20MHz, as a function of applied field. The zero wave vector kinetic coefficient asymtotically approached a constant value, conventional behavior, as the critical temperature was neared from above. Our measurements are consistant with a crossover of the dynamical critical exponent z from 5/2 to ?2 in the region 4πχ≳1, where the dipole interaction dominates.