Wave-Vector-Dependent Susceptibility atT>Tcin a Dipolar Ising Ferromagnet

Abstract

The singular behavior of the susceptibility ${\chi }_T\left(\overrightarrow{\mathrm{Q}}\right)$ near wave vector $\overrightarrow{\mathrm{Q}}=0\mathrm{}$, which is characteristic of long-range dipolar interactions, has been observed in a neutron-scattering study of ${\mathrm{LiTbF}}_4$. Quantitative agreement with mean-field theory is obtained at temperatures $2<\mathrm{}\frac{T}{T_c}<10\mathrm{}$. In a rather broad critical region, $0.01<\mathrm{}\frac{T}{T_c}-1<1\mathrm{}$, the divergent part of ${\chi }_T\overrightarrow{\mathrm{Q}}$ follows a power law $\frac{{\chi }_T(Q_x\to 0)}{\chi _T^{}{}_{}{}^0}=C{(1-\frac{T_c}{T})}^{-\gamma }$ with $C=1.25\mathrm{}\pm 0.13$ and $\gamma =1.13\mathrm{}\pm 0.06$.