Critical Magnetic Neutron Scattering from CoO

Abstract

The critical magnetic neutron scattering from CoO has been measured near the N\'eel temperature ${T}_{\mathrm{N}}$. The diffuse intensity at various wave vectors was assumed proportional to ${A}_{+}{|\frac{T}{{T}_{\mathrm{N}}\ensuremath{-}1}|}^{\ensuremath{-}\ensuremath{\gamma}}$ above ${T}_{\mathrm{N}}$ and ${A}_{\ensuremath{-}}{|\frac{T}{{T}_{N}\ensuremath{-}1}|}^{{\ensuremath{-}\ensuremath{\gamma}}^{\ensuremath{'}}}$ below ${T}_{\mathrm{N}}$. Using the method of Als-Nielsen, we measured the temperature dependence of the critical scattering at several values of $q$ [the displacement from the (111) position in reciprocal space] and used these data to calculate the relative magnitudes of $\ensuremath{\gamma}$ and ${\ensuremath{\gamma}}^{\ensuremath{'}}$. In order to satisfy scaling law requirements we referred our measurements to a rigid lattice by correcting for the large tetragonal contraction below ${T}_{\mathrm{N}}$. We found that ${\ensuremath{\gamma}}^{\ensuremath{'}}=(1.02\ifmmode\pm\else\textpm\fi{}0.02)\ensuremath{\gamma}$, and this suggests that static scaling laws may apply to CoO. In addition we ascertained that $\frac{{A}_{+}}{{A}_{\ensuremath{-}}}\ensuremath{\cong}7.6\ifmmode\pm\else\textpm\fi{}1.5$ in agreement with the linear theory of Schofield, where $\frac{{A}_{+}}{{A}_{\ensuremath{-}}}=6.0\ifmmode\pm\else\textpm\fi{}0.8$ for CoO.