Nanomagnetism, Spindynamics, Spintronics
Nanomagnetism, Electronic Structures & Surfaces
In areas of modern research on the nanoscale, such as magnetoelectronics and spintronics, an understanding of the properties of complex materials in low dimensions is of prime importance. Vector-spin density functional theory provides a unique tool to investigate the electronic and magnetic properties of these systems. It facilitates the study of magnetic order, magnetization direction, ordering temperatures, transport properties, etc. of thin films, surfaces, and nanostructures.
The discovery of giant and tunnel magnetoresistance (GMR and TMR), in particular the fact that transport properties through an interface depend strongly on the magnetic properties of the interface itself, has revolutionized modern device technology. The quantum mechanical description of transport through an interface allows a detailed understanding of the magnetic tunnel junctions used in spin and magnetoelectronics. A basic concept in this description is the complex band structure shown here for Cu (100). It contains not only the "normal'' (Bloch) states of the solid (shown in black), but also the "evanescent'' states (shown in colour) responsible for the transport process.
( D. Wortmann)
Electronic Excitations, Spin Dynamics
The principal way to gain knowledge about a material is to study its reaction to various external factors, such as light irradiation or magnetic fields. As the perturbation moves the system out of equilibrium, it serves first and foremost as a probe for excited states. A proper microscopic treatment of these processes is possible within many-body perturbation theory, which takes both the Coulomb interaction and the coupling to the external field explicitly into account. Theoretical simulations can thus be directly related to experimental spectroscopy and allow us to calculate electronic band structures or spin-wave spectra with great accuracy. Moreover, dynamic properties such as the finite lifetime of elementary excitations are also accessible for study.
Complex magnetism in nanostructures and RKKY interactions
Tiny magnets made up of only a few atoms could provide foundation for future information technology, making it faster and less energy consuming with new functionalities. To achieve this goal, it is important to understand the physical and more precisely the magnetic interactions within atomic building blocks or between them. We are, for example, interested in the way magnetic frustration triggers complex magnetic structures in small clusters. This is a formidable theoretical task since several parameters can impact on the magnetic ground states as well as the magnetic excitation spectrum: The chemical nature of nanostructure, type of substrate, structure, orientation, spin-orbit coupling. Moreover we are focusing on drawing theoretically a map of the short and long range magnetic interactions (RKKY-type) between several kind of adatoms and mediated via the electronic states of the substrate.
A strong effort is devoted to unravel the magnetic structures of the mediating electronic states that can acquire complex magnetic textures of skyrmionic nature. When possible, comparison is made to recent state of the art measurements provided with scanning tunneling microscopy helping to improve our theoretical approach based on density functional theory combined with multiple scattering theory as expressed within the Korringa-Kohn-Rostoker Green function method. We have learned from our investigations that as soon as an atom is added or removed, the magnetic properties of entire nanomagnets can change radically.
More details: Funsilab