Theory of Spin Waves in the Heavy Rare Earth Metals

Abstract

<p> A theory of spin waves for the spin structures found in the rare earth metals of hcp crystal structure is described. The theory is developed for the conical spiral spin structure which contains the planar spiral, the nonplanar ferromagnet and the planar ferromagnet as special cases. Included in the Hamiltonian are isotropic and anisotropic exchange interactions, single-ion crystal field terms, and magnetoelastic terms, both of the single-ion type and the two-ion type. Equations of motion for the spin operators are linearized with the help of the random phase approximation which makes it possible to express some spin-wave interaction effects in terms of powers of the reduced magnetization. Expressions for the spin-wave energies are given for the four structures under consideration.</p>