Neutron scattering study of the spin dynamics and spin-wave form factor of chromium

The spin excitations in a single crystal of ${\mathrm{Cr}}_{0.98}$ ${\mathrm{Mn}}_{0.02}$ have been studied by inelastic neutron scattering. High-resolution triple-axis spectrometer measurements have yielded a value of the spin-wave velocity at $\frac{T}{T_N}\simeq 0.5$ of (1.30 ± 0.15) × ${10}^7$ cm/sec in good agreement with earlier measurements. The excitation strength drops extremely rapidly in the vicinity of $T_N$ and decreases approximately linearly above $T_N$. The spin-wave form factor has been measured below and above $T_N$ by measuring the spin-wave intensity at various superlattice points, and is found to agree to within experimental error with the static spin form factor. The implications of these results for the theory of itinerant electron antiferromagnetism are discussed.