Microscopic theory of spin arrangements and spin waves in very thin ferromagnetic films.

Abstract

We present theoretical studies of the classical ground-state spin configuration and spin waves, in very thin ferromagnetic films, with thickness that ranges from a monolayer to a few tens of layers. The analyses are based on a microscopic model that includes dipolar and exchange interactions between the spins, surface (or interface) anisotropy of single-site character quadratic and quartic in the spin components, along with an external magnetic field applied at an arbitrary direction with respect to the film normal. Issues explored include the nature of spin canting induced by surface anisotropy in ultrathin (few-atomic-layer) films, and in films with thicknesses of up to 100 layers. Also, we explore the nature of spin waves in ultrathin films, in the presence of spin canting, and in thicker films with attention to the interplay between dipolar and exchange contributions to the excitation energy. Most particularly, in the thicker films, we examine the transition from the dipole-dominated Damon-Eshbach waves to the exchange-dominated surface spin waves that emerge from the Heisenberg model.