Critical Behavior of the Heisenberg Ferromagnets EuO and EuS

Neutron-scattering measurements have been made of the critical parameters of the simple Heisenberg ferromagnets EuO and EuS. Values of the critical exponents β and ν and the amplitudes of B and F describing, respectively, the reduced magnetization and the inverse correlation range (above Tc) are in good accord with theory. The measured values of the exponent γ, describing the static susceptibility, support the recent prediction that γ≈1.40 in a simple nearest-neighbor Heisenberg ferromagnet. The scaling relation between β, ν, and γ is fulfilled.