Magnetic Critical Phenomena in MnP by Neutron Scattering

Three‐crystal inelastic neutron scattering measurements have been carried out on a single crystal of MnP in the critical region. The compound is ferromagnetic below its ordering temperature of 291.5°K. The results of the experiments have demonstrated that for T<T_c, there exists a striking dissimilarity between the profiles observed for MnP on one hand and iron and nickel on the other. We have observed for the first time the diffusive fluctuations in a ferromagnet for T<T_c. These results should be contrasted with those that were previously obtained for iron and nickel. For iron and nickel, these diffusive modes have never been clearly observed. The characteristic frequency of the critical fluctuations Γ(κ, ζ) for T=T_c is found to be reliably described by the relation Γ(0, ζ) ∝ζ^x, where x=2.57±0.11, and ζ is the reduced wave vector. This result is in excellent agreement with the prediction made from dynamic scaling theory. For the isotropic ferromagnet, the dynamic scaling principle predicts a critical exponent of $\frac{5}{2}$ .