Both magnetoelastic and neutron-diffraction studies have been performed on Cr-Al single crystals containing 1.2, 1.9, and 2.6 at. % Al. These concentrations lie in a controversial region of the magnetic phase diagram. For the crystals containing 1.2 and 1.9 at. % Al the transition at the Néel point is from a paramagnetic to an incommensurate spin-density-wave (ISDW) state while it is from the paramagnetic to a commensurate (C) SDW state for Cr+2.6 at. % Al. All magnetic transitions are observed as second-order phase changes within our experimental resolution. No ISDW-CSDW transition was observed in any of the crystals, and no evidence was found for the existence of mixed ISDW and CSDW phases in the alloys, as previously predicted. The temperature dependence of the elastic constants is described fairly well by existing thermodynamic models, while the magnetization ${\mathit{M}}^2$(T)/${\mathit{M}}^2$(0) of Cr + 1.9 at. % Al and Cr+2.6 at. % Al varies as [1-α(T/${\mathit{T}}_{\mathit{N}}$${)}^2$+δ(T/${\mathit{T}}_{\mathit{N}}$${)}^4$] at T<${\mathit{T}}_{\mathit{N}}$. The values of α and δ compare fairly well with values obtained from magnetovolume data.

• Received 12 December 1991

DOI:https://doi.org/10.1103/PhysRevB.45.10473