Markus Hoffmann

Tailoring magnetic skyrmions in ultra-thin transition metal films

Skyrmions in magnetic materials offer attractive perspectives for future spintronic applications since they are topologically stabilized spin structures on the nanometre scale, which can be manipulated with electric current densities that are by orders of magnitude lower than those required for moving domain walls. So far, they were restricted to bulk magnets with a particular chiral crystal symmetry greatly limiting the number of available systems and the adjustability of their properties. Recently, it has been experimentally discovered that magnetic skyrmion phases can also occur in ultra-thin transition metal films at surfaces. Here we present an understanding of skyrmions in such systems based on first-principles electronic structure theory. We demonstrate that the properties of magnetic skyrmions at transition metal interfaces such as their diameter and their stability can be tuned by the structure and composition of the interface and that a description beyond a micromagnetic model is required in such systems.

Antiskyrmions stabilized at interfaces by anisotropic Dzyaloshinskii-Moriya interactions

Chiral magnets are an emerging class of topological matter harboring localized and topologically protected vortex-like magnetic textures called skyrmions, which are currently under intense scrutiny as an entity for information storage and processing. Here, on the level of micromagnetics we rigorously show that chiral magnets can not only host skyrmions but also antiskyrmions as least energy configurations over all non-trivial homotopy classes. We derive practical criteria for their occurrence and coexistence with skyrmions that can be fulfilled by (110)-oriented interfaces depending on the electronic structure. Relating the electronic structure to an atomistic spin-lattice model by means of density functional calculations and minimizing the energy on a mesoscopic scale by applying spin-relaxation methods, we propose a double layer of Fe grown on a W(110) substrate as a practical example. We conjecture that ultra-thin magnetic films grown on semiconductor or heavy metal substrates with C2v symmetry are prototype classes of materials hosting magnetic antiskyrmions.Skyrmions, localized defects in the magnetization, can be stabilised in materials by the Dzyaloshinskii-Moriya interaction (DMI). Hoffmann et al. predict that, when the DMI is anisotropic, antiskyrmions can be formed and coexist with skyrmions, enabling studies and exploitation of their interactions.