Low-temperature thermal expansion of single-Qchromium and of dilute antiferromagneticCrV alloys

Measurements of the uniaxial thermal expansion of a Cr single crystal having a single spin-density-wave vector Q show that the large negative term linear in temperature in the expansivity at low temperatures has an anisotropy of about 50%. This linear term is found to increase in magnitude in multidomain antiferromagnetic CrV alloys as the impurity concentration increases, although the N\'eel temperature decreases. The corresponding positive magnetovolume measured by comparison with paramagnetic Cr₉₅{V}₅$ is found to scale with the square of the N\'eel temperature, as predicted if this magnetovolume arises from expansion of the lattice in the magnetic state to minimize the kinetic-energy cost of ordering.