Lattice Anisotropy in Antiferromagnetic Chromium

Thermal expansion and magnetostriction measurements on single-$\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}}$ single-crystal chromium give the lattice parameter ratios in the orthorhombic phase below the N\'eel temperature and through the transition to the tetragonal phase at the spin-flip temperature, ${T}_{F}=122\ifmmode^\circ\else\textdegree\fi{}$K. The $\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}}$ direction is the longest axis at 300\ifmmode^\circ\else\textdegree\fi{}K and becomes the shortest axis below \ensuremath{\sim}200\ifmmode^\circ\else\textdegree\fi{}K. The anisotropic discontinuities in length at ${T}_{F}$ result in a net volume dilatation, 1.4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ with decreasing temperature.