Measurements of the magnetic excitations above T c in iron and nickel (invited)

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Abstract
High‐resolution neutron scattering measurements, utilizing full polarization analysis techniques, have been carried out to explore the nature of the magnetic response above Tc in these itinerant ferromagnets. Large isotopically enriched single crystals were employed in order to obtain reliable determinations of the scattering function S(q,E). The scattering in Ni is found to evolve in a continuous fashion from the well‐known spin diffusion response at small wave vectors q to a response with peaks centered at ±E at larger q, in agreement with our original work. The ratio of the observed widths of these spin waves to the spin‐wave energies, as determined directly from measurements at constant q, is found to decrease with increasing ‖q‖ as expected. We also show that the recent measurements by Shirane and collaborators were taken with resolution which was too coarse to observe these spin‐wave excitations.