Observation of crossover in the dynamic exponent z in Fe and Ni

Time-differential perturbed angular correlations have been determined with use of the dynamical critical exponent z for Fe and Ni. In both systems, crossover from z=2.5 to z=2.0 is observed as TTC. The value z=2.5 (d=3 Heisenberg model) has been previously observed in neutron-scattering experiments; the value z=2.0 (order-parameter-nonconserving models), in hyperfine-interaction experiments. Thus, the existence of two distinct kinds of dynamic critical behavior, each corresponding to a different universality subclass, is confirmed. © 1980 The American Physical Society.