DETERMINATION OF THE UNIVERSALITY CLASS OF GADOLINIUM

We resolve a long-standing puzzle for the static and dynamic critical behavior of gadolinium by a combined theoretical and experimental inve stigation, It is shown that the spin dynamics of a ferromagnet with hc p lattice structure and a spin-spin interaction given by both exchange and dipole-dipole interaction belongs to a new dynamic universality c lass, model J. Comparing results from mode coupling theory with resul ts from three different hyperfine interaction probes we find quantitat ive agreement.