Thermal-expansion and elastic constants of dilute Cr-Al alloys

The thermal-expansion and elastic constants of dilute Cr-Al alloys containing 0.67, 1.06, 1.70, 2.19, 2.74, and 3.22 at.% Al are reported in the temperature range $4 2$ at.% Al. The magnetic contribution to B at 0 K reaches a large peak value of about 1.1×{}10¹¹ Nm^-2 for alloys near 2 at.% Al. It is concluded that antiferromagnetism is not suppressed for $2<c<4$ at.% Al in contrast with suggestions based on previous resistivity and susceptibility measurements. The magnetovolume, Δω, of all the alloys as well as of pure chromium is found to vary as Δω(T)=a+bT²+cT⁴ at T<TN. This type of relation is predicted by itinerant-electron theories which, however, fail to produce the correct temperature variation of the magnetic contribution (ΔB) to B. The measured values of Δω and ΔB are used to calculate the concentration dependence of dTNdp. It decreases rapidly with Al concentration in the range $2<c<4$ at.% Al where the absence of resistivity anomalies at TN previously precluded the direct determination of dTNdp.