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

• Received 23 July 1971

DOI:https://doi.org/10.1103/PhysRevLett.27.741