Spin-Wave Spectrum of Yttrium Iron Garnet

The spin-wave spectrum of yttrium iron garnet is treated using a Hamiltonian involving nearest-neighbor a-a, d-d, and a-d isotropic exchange interactions. Values of the exchange constants are estimated from the molecular field constants of Pauthenet. Anisotropy and magnetic dipole-dipole interactions are neglected. Twenty spin-wave modes are found, and their energies calculated at points of cubic symmetry in k space. The dispersion relation of the single "acoustical" spin-wave mode is found to agree with the value previously reported by Meyer and Harris.