Direct observation of spin waves aboveTCfor nickel

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Abstract
Inelastic-neutron-scattering measurements with the constant-q technique have been used to characterize the energy response of the scattering in paramagnetic nickel. At small wave vectors q, the scattering peaks at zero energy, indicative of spin diffusion, but at larger q the scattering maximizes at finite ±E demonstrating that the spectral response has propagating character. The relative width ΔE/E of the excitation decreases with increasing ‖q‖ as expected, with the excitation becoming well defined as its energy becomes comparable with kT.