Spin waves

The method of choice for measuring spin-wave dispersion relations is inelastic neutron scattering. The entire set ofω(q) curves can be mapped out with a tripleaxis spectrometer, as shown for Gd in Fig. 1. Other methods give less complete information. Inelastic light scattering or standing spin-wave resonance, for example, are restricted to the long-wavelength region of small momentum transfer.

Figure 1: Spin-wave dispersion relations for Gd measured by inelastic neutron scattering. Since the anisotropy is negligible, the spin-wave dispersion relation is quadratic near q = 0.