Scattering of Polarized Neutrons by Spin Waves in Magnetite and Yttrium Iron Garnet

We have employed the neutron diffraction technique to study the inelastic scattering of polarized 1.08 {} neutrons by magnetic spin waves in magnetite and in yttrium iron garnet (YIG). Measurements were made for the cases when the magnetite and YIG scatterers were oriented near the positions for (111) and (220) Bragg reflections, respectively. Two new and widely applicable methods are given for determining the parameter D appearing in the usual expression Dq² (q = magnon wave number) for the energies of long-wavelength acoustic spin waves in usual ferromagnets and ferrimagnets. These methods are based on a comparison between experimental and calculated intensity ratios of magnetic diffuse reflections measured by the polarized neutron technique. The value D=0.49±0.04 eV ² was found for magnetite using one of these methods; for YIG, the respective values D=0.26±0.01 eV ² and D=0.26±0.02 eV ² were obtained by the aforementioned two methods.