Long-Range Order and Critical Scattering of Neutrons below the Transition Temperature inβ-Brass

The temperature dependence of long-range order 〈Pₒ〉 has been determined from the temperature variation of a superlattice Bragg reflection. The results fitted a power law 〈Pₒ〉∝(Tc-T)^β with Tc the critical temperature and β=0.305±0.005, in agreement with the theoretical prediction 0.303<β<0.318 obtained from a comparison of the measured line profiles of the (1,0,0) superlattice reflection at 15.5 and 2.2^∘{} below Tc. The ratio between the susceptibilities χ⁺(ΔT) and χ^-(ΔT) ΔT deg below and above Tc was found to be 5.5±{}2.0 at ΔT=4.4^∘ and 8.5±{}3.0 at ΔT=2.1^∘. The Ising-model theory predicts the ratio to be 5.2 independent of ΔT.