Critical neutron scattering from the Heisenberg ferromagnets EuO and EuS

Abstract The magnetic neutron scattering from isotopically enriched powders of EuO and EuS near their Curie temperatures has been studied. Results of the critical exponents for the static properties in standard notation were magnified image Spin wave scattering at T << T c confirmed that EuO has predominantly nearest neighbor interaction only with J 1 = 0.602 ± 0.008 K, J 2 = 0.155 ± 0.014 K whereas in EuS J 1 = 0.234 ± 0.016 K, J 2 = 0.098 ± 0.014 K. The renormalization of spin wave energies were determined. The characteristic frequency at T = T c , ω c ( q , k = 0), obeyed the 5/2 law predicted by scaling and with amplitudes for both EuO and EuS which are in remarkable agreement with the mode‐mode coupling calculation of Riedel and Wegner. Above T c the ratio ω c ( q , k )/ω c ( q , k = 0) versus k / q displayed a pronounced minimum at k / q ≈︁ 1.5 as predicted by Resibois and Piette.