Spin dynamics in the cubic Heisenberg ferromagnet EuS

Using the inelastic-neutron-scattering technique, we have undertaken an extensive study of the spin dynamics in EuS. The experiments were performed on a ¹⁵³EuS single crystal with the scattering vector →q along the [100] direction. The q values extended over the range between 0.11 and 1.06 ^-1, and the temperatures ranged from 1.2 to 50 K(=3Tc). It was found that spin-wave renormalization theory holds well up to 0.8Tc. For temperatures above Tc and up to the highest temperatures of our experiments, the line shapes are well described by the recently developed correlation theories. From the q dependence of the linewidth of the dynamical response at T=Tc, a dynamical scaling exponent $z=2.09(6)$ was deduced. The deviation from the pure Heisenberg value of z=5/2 is attributed to the dipolar interactions.