Magnetization Configurations and Reversal in Small Magnetic Elements

The in-plane orientation of the magnetization in the center of domain walls is measured in Co/Ir(111) as a function of Co thickness via scanning electron microscopy with polarization analysis. Uncapped, thermally evaporated cobalt on an Ir(111) single-crystal surface is imaged in situ in ultrahigh vacuum. The initial pseudomorphic growth with an atomically flat interface of cobalt on iridium ensures comparability to theoretical calculations and provides a study of an interface that is as ideal as possible. Below a cobalt thickness of 8.8 monolayers, the magnetic domain walls are purely N\'eel oriented and show a clockwise sense of rotation. For larger thicknesses the plane of rotation changes and the domain walls show a significant Bloch-like contribution, allowing one to calculate the strength of the Dzyaloshinskii-Moriya interaction (DMI) from energy minimization. From the angle between the plane of rotation and the domain-wall normal an interfacial DMI parameter ${D}_{\mathrm{s}}=\ensuremath{-}(1.07\ifmmode\pm\else\textpm\fi{}0.05)\phantom{\rule{4pt}{0ex}}\mathrm{pJ}/\mathrm{m}$ is determined, which corresponds to a DMI energy per bond between two Co atoms at the interface of ${d}_{\mathrm{tot}}=\ensuremath{-}(1.04\ifmmode\pm\else\textpm\fi{}0.05)\phantom{\rule{4pt}{0ex}}\mathrm{meV}$.

Measuring the Dzyaloshinskii-Moriya interaction of the epitaxial Co/Ir(111) interface

Using time-resolved scanning electron microscopy with polarization analysis (TR-SEMPA) the dynamics of magnetic vortices and antivortices in a cross-tie wall is investigated. Under quasistatic external field drive both quasiparticles oscillate at opposite phase to each other (in analogy to an optical mode). An additional common motion, which stems from the finite boundary conditions in a patterned FeCoSiB rectangle, is observed (in analogy to an acoustic mode), leading in total to a stronger field-dependent displacement for the vortices compared to the antivortices. Both types of magnetic solitons are mutually coupled via the minimization of the total magnetic energy of the structure. It is shown that the TR-SEMPA results can be explained via coupling in the framework of micromagnetic simulations and that the coupling constants can be extracted. The motion is composed from the contributions of the two terminating vortices and a mutual vortex-antivortex coupling along the chain.

Coupling between vortices and antivortices in a cross-tie wall studied by time-resolved SEMPA

In this work, we study modifications of the spectrum of fermions interacting with kinklike structures in two-dimensional spacetime. We consider the Yukawa coupling between fermions and scalar fields that engender nontrivial internal structure and investigate how the fermion spectra change in terms of the parameters that control the kinklike configuration and the Yukawa coupling. We consider models that allow the internal structure of the kinklike solution to respond to the presence of a geometrical constriction and show the fermion spectra may also appear directly affected by the constriction. The main results are of current interest and may be used to propose the construction of electronic devices capable of engendering new effects at the nanometric scale.

Fermions in the presence of topological structures under geometric constrictions

Entail the new path for permanent magnets: Free-standing Hf-Co thin films

Perpendicularly magnetized nanowires exhibit distinct domain wall types depending on the geometry. Wide wires contain Bloch walls, and narrow wires N\'eel walls. Here, the transition region is investigated by direct imaging of the wall structure using high-resolution spin-polarized scanning electron microscopy. An achiral intermediate wall type is discovered that is unpredicted by established theoretical models. With the help of micromagnetic simulations, the formation of this wall type is explained.

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Achiral tilted domain walls in perpendicularly magnetized nanowires

Starting from an ultrathin Fe film grown epitaxially on top of a GaAs(001) substrate, we show that freestanding structures can be created by ion-beam treatment. These structures are single-crystalline blisters and only a few nanometers thick. Anisotropic stress in the rim of a blister induces magnetic domain states magnetized in the direction normal to the blister edge. Experimental evidence is provided that the lateral size can be confined by starting from a nanostructured template.

B. Boehm

Papers

Achiral tilted domain walls in perpendicularly magnetized nanowires

Freestanding single-crystalline magnetic structures fabricated by ion bombardment