Midway evaluation in Physics - Hendrik Schrautzer

Title:
Ordering in multistable magnetic nanostructures

Doctoral committee: 
Pavel Bessarab, Research Specialist in the Science Institute, University of Iceland.
Dr. Snorri Þorgeir Ingvarsson, Professor at the Faculty of Physical Sciences, University of Iceland.
Dr. Stefan Heinze, Professor at the Institute of Theoretical Physics and Astrophysics, University of Kiel.
Dr. Hannes Jónsson, Professor at the Faculty of Physical Sciences, University of Iceland.

Abstract in English:
Magnetic nanosystems exhibiting co-existing magnetic orders are of great interest for fundamental science and technological applications, but their characterization is challenging due to the complexity of the energy landscape. In our project we develop a theoretical framework for systematic identification of complex orderings in multistable magnetic systems. The key ingredient of the methodology is an original theoretical approach that combines global optimization based on recursive traversing between energy minima via saddle points on the energy surface of a magnetic system, and harmonic rate theory enabling calculations of the lifetime of the magnetic states at a given temperature based on intrinsic properties of the system. In this talk, the status of the project will be discussed. Development and implementation of the saddle point search method for magnetic systems will be reported. In contrast to previous methods based on computationally costly calculations of the Hessian of the energy of the system, our implementation takes advantage of evaluating only the gradient, which makes the method applicable to large systems, including three-dimensional structures. We will demonstrate the application of the method to various two- and three-dimensional systems, including those parametrized using density functional theory calculations. This will showcase the multistability of different spin textures, such as skyrmions, antiskyrmions, skyrmioniums, chiral bobbers, and globules.