Polarized-beam study of the paramagnetic scattering from bcc iron

Reliable magnetic scattering cross sections are obtained for bcc Fe at T=1.02Tc and 1.06 Tc using polarized neutrons and polarization analysis. The constant-q measurements cover a q range of 0.1-0.6 -1 with an energy range extending up to 50 meV. These scans consist of broad energy distributions centered at zero energy with no peaks observed at finite-energy transfers, in contrast to the results reported by Lynn. A simple paramagnetic scattering function S(q,)[1(12+q2)][(2+2)] is shown to describe the iron cross sections quantitatively, and in absolute units, for the q and energy range specified above. The peaks observed in constant-energy scans are simply energy slices of the paramagnetic scattering function and thus should not be interpreted as spin-wave peaks. We conclude that in the (q,) region covered in our polarized beam studies, neither propagating spin waves nor giant short-range magnetic order exist in Fe above Tc.