Diffuse magnetic elastic scattering of neutrons from Cr-Fe and Cr-Co alloys

Abstract

The diffuse magnetic elastic scattering from powder samples of Cr‐12 at % Fe and Cr‐10 at % Co has been obtained at temperatures above and below T_N. Polarized neutrons and polarization analysis were used on the D5 instrument at I. L. L. Grenoble to obtain a unique determination of the magnetic scattering. For the Cr‐Fe alloy forward scattering was observed both above and below T_N without significant change in magnitude or Q‐dependence. The magnitude was consistent with that expected from susceptibility measurements. The fall‐off with increasing Q was more rapid than that anticipated for a typical 3d form factor tending towards zero at (sinϑ)/λ∼0.15 Å⁻¹. In contrast, the response of the cobalt‐containing alloy was suppressed below T_N although of a similar form to the Fe alloy above T_N. This suppression could be associated with a locking of the Co moments to the SDW. The incoming neutrons (λ = 0.84 Å) have energy ∼115 meV and with an analyser‐detector window of 20 meV any locking of the Fe moments (with coupling constants of ≲4 meV) would not be detected.