Spin waves in nanosized magnetic films

TL;DR

This paper investigates spin wave excitations in nanosized magnetic films using the Heisenberg model, deriving dispersion relations, resonance spectra, and damping characteristics, and proposes spin-wave devices for microwave to Terahertz applications.

Contribution

It introduces a first-principles derivation of Landau-Lifshitz equations for thin films and analyzes spin wave damping mechanisms specific to nanosized magnetic structures.

Findings

Spin wave dispersion relations were obtained for thin and multilayer magnetic films.

Damping of spin waves is mainly due to magnetic dipole interactions in thick films.

Thin films exhibit low damping and enable spin-wave device applications.

Abstract

We have studied spin excitations in nanosized magnetic films in the Heisenberg model with magnetic dipole and exchange interactions by the spin operator diagram technique. Dispersion relations of spin waves in thin magnetic films (in two-dimensional magnetic monolayers and in two-layer magnetic films) and the spin-wave resonance spectrum in N-layer structures are found. For thick magnetic films generalized Landau-Lifshitz equations are derived from first principles. Landau-Lifshitz equations have the integral (pseudodifferential) form, but not differential one. Spin excitations are determined by simultaneous solution of the Landau-Lifshitz equations and the equation for the magnetostatic potential. For normal magnetized ferromagnetic films the spin wave damping has been calculated in the one-loop approximation for a diagram expansion of the Green functions at low temperature. In thick magnetic films the magnetic dipole interaction makes a major contribution to the relaxation of long-wavelength spin waves. Thin films have a region of low relaxation of long-wavelength spin waves. In thin magnetic films four-spin-wave processes take place and the exchange interaction makes a major contribution to the damping. It is found that the damping of spin waves propagating in magnetic monolayer is proportional to the quadratic dependence on the temperature and is very low for spin waves with small wavevectors. Spin-wave devices on the base of nanosized magnetic films are proposed -- tunable narrow-band spin-wave filters with high quality at the microwave frequency range and field-effect transistor (FET) structures contained nanosized magnetic films under the gate electrode. Spin-wave resonances in nanosized magnetic films can be used to construct FET structures operating in Gigahertz and Terahertz frequency bands.