Spin dynamics in Tb studied by critical neutron scattering

The inelasticity of the critical neutron scattering in Tb was measured at and above the Neel temperature. In the hydrodynamic region the line width Gamma (q=0, kappa 1 )=C kappa z 1 , with z=1.4+or-0.1 and c=4.3+or-0.3 meVAA z . This result deviates from the conventional theory, which predicts that Gamma (q=0, kappa 1 ) is inversely proportional to the static susceptibility, that is z=2. In the critical region it was found that Gamma (q, kappa 1 =0)= Lambda q delta , with delta =2.0+or-0.1 and Lambda =7.5+or-0.7 meVAA delta . The prediction of the dynamical scaling laws that delta =z is thus not fulfilled.