Center for Functional Nanomaterials Seminar

Magnons or spin-waves are elementary collective excitations of magnets. At the energy scale larger than anisotropy constant their energies are determined by the exchange interaction and their life time is limited by excitations of single electron spin flips (Stoner states). The latter process is known as Landau damping. Little is known about the properties of spin-waves on the lenght scale of nanometers and the role the Stoner states play there except for causing the attenuation. On the other hand, the excitations are the key to understand the dynamics of the magnetization and the thermodynamics of magnets. Magnons and other magnetic excitation can provide an alternative coupling mechanism in high temperature superconductors.

I will present an ab initio method which will allow us to compute the dynamic magnetic susceptibility of complex metallic magnets and thus access the information about both the energies and life-time of magnons. The formalism is based in the linear response density functional theory and our novel computer implementation relies on the Korringa-Kohn-Rostoker Green’s function method.

We will discuss the applications of the method to half-metallic Heusler compounds. In these materials low energy spin-waves cannot decay via Landau mechanism and can acquire life times orders of magnitude longer than their counterparts in normal metallic magnets. Next, we will focus on magnons in thin metallic films, outlining the possibility of using standing spin-wave trapped between the surface of the film and the interface to gain a precise control over the precession of spins. We will show how the Landau damping leads to the mixing of natural spin-waves modes of the system. The attenuation is normally enhanced when the film is supported on a non-magnetic metallic substrate and the details of this effect will be discussed.