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

The temperature dependence of long-range order $〈P_{\mathrm{o}}〉$ has been determined from the temperature variation of a superlattice Bragg reflection. The results fitted a power law $〈P_{\mathrm{o}}〉\propto {(T_c-T)}^{\beta }$ with $T_c$ the critical temperature and $\beta =0.305\mathrm{}\pm 0.005$, in agreement with the theoretical prediction $0.303<\mathrm{}\beta <0.318\mathrm{}$ obtained from a comparison of the measured line profiles of the (1,0,0) superlattice reflection at 15.5 and 2.2° below $T_c$. The ratio between the susceptibilities ${\chi }^{+}\left(\Delta T\right)$ and ${\chi }^{-}\left(\Delta T\right) \Delta T$ deg below and above $T_c$ was found to be 5.5±2.0 at $\Delta T={4.4}^{\circ }$ and 8.5±3.0 at $\Delta T={2.1}^{\circ }$. The Ising-model theory predicts the ratio to be 5.2 independent of $\Delta T$.