Critical magnetic scattering from the Heisenberg ferromagnet EuS

The paramagnetic scattering from the insulating, isotropic ferromagnet EuS is investigated at TC along the [111] direction by means of inelastic neutron scattering. The energy width of the quasielastic scattering is proportional to qz with z=2.54±0.10, in good agreement with the predictions of dynamical scaling theory (z=2.5). z is, however, significantly larger than the value deduced from measurements along the [100] direction (z∼2.2). Near the zone boundary the magnetic scattering exhibits shoulders the shapes of which deviate from theoretical predictions based on the Heisenberg model.