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 1.06Tc using polarized neutrons and polarization analysis. The constant-q measurements cover a q range of 0.1-0.6 \AA{}-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,$\omega$)$\propto$[1($̨appa$21+q2)][$\Gamma$($\Gamma$2+$\omega$2)] is shown to describe the iron cross sections quantitatively, and in absolute units, for the q and energy range specified above. The peaks observed in constant-energy scans are simply energy slices of the paramagnetic scattering function and thus should not be interpreted as spin-wave peaks. We conclude that in the (q,$\omega$) region covered in our polarized beam studies, neither propagating spin waves nor giant short-range magnetic order exist in Fe above Tc.     «

Reliable magnetic scattering cross sections are obtained for bcc Fe at T=1.02Tc and 1.06Tc using polarized neutrons and polarization analysis. The constant-q measurements cover a q range of 0.1-0.6 \AA{}-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,$\omega$)$\propto$[1($̨appa$21+q2...     »