Corina Etz

Topological excitations in a kagome magnet

Chirality--that is, left or right handedness--is present in many scientific areas, and particularly in condensed matter physics. Inversion symmetry breaking relates chirality with skyrmions, which are protected field configurations with particle-like and topological properties. Here we show that a kagome magnet, with Heisenberg and Dzyaloshinskii-Moriya interactions, causes non-trivial topological and chiral magnetic properties. We also find that under special circumstances, skyrmions emerge as excitations, having stability even at room temperature. Chiral magnonic edge states of a kagome magnet offer, in addition, a promising way to create, control and manipulate skyrmions. This has potential for applications in spintronics, that is, for information storage or as logic devices. Collisions between these particle-like excitations are found to be elastic at very low temperature in the skyrmion-skyrmion channel, albeit without mass-conservation. Skyrmion-antiskyrmion collisions are found to be more complex, where annihilation and creation of these objects have a distinct non-local nature.

Atomistic spin dynamics of low-dimensional magnets

We investigate the magnetic properties of a range of low-dimensional ferromagnets using a combination of first-principles calculations and atomistic spin dynamics simulations. This approach allows ...

Magnetic properties of single atoms of Fe and Co on Ir(111) and Pt(111)

In using the fully relativistic versions of the embedded cluster and screened Korringa-Kohn-Rostoker methods for semi-infinite systems the magnetic properties of single adatoms of Fe and Co on Ir(111) and Pt(111) are studied. It is found that for Pt(111) Fe and Co adatoms are strongly perpendicularly oriented, while on Ir(111) the orientation of the magnetization is only out of plane for a Co adatom; for an Fe adatom it is in plane. For comparison, the so-called band energy parts of the anisotropy energy of a single layer of Fe and Co on these two substrates are also shown. The obtained results are compared to recent experimental studies using, e.g., the spin-polarized STM technique.

Ab initio electronic structure and magnetism in Sr2XMoO6 (X = Fe or Co) double perovskite systems: a GGA and GGA + U comparative study

Using the full potential linearized augmented plane wave ab initio method, we investigate bulk magnetic properties of Sr2XMoO6 (X = Fe, Co) double perovskites by comparing the results obtained with the generalized gradient approximation (GGA) and GGA+U methods in order to discuss their magnetic configuration in relation with the experiments. We show that both methods lead to significantly different results and that a good agreement with experimental results—antiferromagnetic insulator for X = Co—can be obtained only when the GGA+U method is used. For X = Fe, we exhibit the role played by oxygen vacancies in the stabilization of a negative magnetic moment on the Fe antisite with preserved half-metallicity. We show that such a negative moment can be obtained only when an oxygen vacancy occurs in the direct neighbourhood of the Fe antisite with the GGA+U method.

Atomistic spin dynamics and surface magnons

Atomistic spin dynamics simulations have evolved to become a powerful and versatile tool for simulating dynamic properties of magnetic materials. It has a wide range of applications, for instance switching of magnetic states in bulk and nano-magnets, dynamics of topological magnets, such as skyrmions and vortices and domain wall motion. In this review, after a brief summary of the existing investigation tools for the study of magnons, we focus on calculations of spin-wave excitations in low-dimensional magnets and the effect of relativistic and temperature effects in such structures. In general, we find a good agreement between our results and the experimental values. For material specific studies, the atomistic spin dynamics is combined with electronic structure calculations within the density functional theory from which the required parameters are calculated, such as magnetic exchange interactions, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya vectors.

Electronic structure, cohesive properties and magnetism of SrRuO3; a theoretical investigation

We have performed an extensive test of the ability of density functional theory within several approximations for the exchange-correlation functional, local density approximation + Hubbard U, and l ...

First-principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys

Heusler alloys have been intensively studied due to the wide variety of properties that they exhibit. One of these properties is of particular interest for technological applications, i.e., the fac ...

Thermally driven domain-wall motion in Fe on W(110)

It has recently been shown that domain walls (DWs) in ferromagnets can be moved in the presence of thermal gradients. In this work we study the motion of narrow domain walls in low-dimensional systems when subjected to thermal gradients. The system chosen is a monolayer of Fe on W(110) which is known to exhibit a large anisotropy while having a soft exchange, resulting in a very narrow domain wall. The study is performed by means of atomistic spin dynamics simulations coupled to first-principles calculations. By subjecting this system to thermal gradients we observe a temperature-dependent movement of the domain wall. The thermal gradient always makes the domain wall move towards the hotter region of the sample with a velocity proportional to the gradient. Our material specific study is complemented by model simulations to discern the interplay between the thermal gradient, magnetic anisotropy, and the exchange interaction and shows that the larger DW velocities are found for materials with broader domain-wall width. The relatively slow DW motion of the Fe/W(110) system is hence primarily caused by its narrow domain-wall width, which results from its large magnetic anisotropy and soft exchange.

Accelerating the switching of magnetic nanoclusters by anisotropy-driven magnetization dynamics

In this work, the magnetization dynamics of clusters supported on nonmagnetic substrates is shown to exhibit a complex response when subjected to external magnetic fields. The field-driven magnetization reversal of small Co clusters deposited on a Cu(111) surface has been studied by means of first-principles calculations and atomistic spin dynamics simulations. For applied fields ranging from 1 to 10 Tesla, we observe a coherent magnetization reversal with switching times in the range of several tenths of picoseconds to several nanoseconds, depending on the field strength. We find a nonmonotonous dependence of the switching times with respect to the strength of the applied field, which we prove has its origin in the complex magnetic anisotropy landscape of these low-dimensional systems. This effect is shown to be stable for temperatures around 10 K, and is possible to realize over a range of exchange interactions and anisotropy landscapes. Possible experimental routes to achieve this unique switching behavior are discussed.

Evanescent exchange magnons in a 1D magnonic crystal

We investigate the transport properties of propagating and non-propagating exchange modes in a 1D magnonic crystal composed of stacked alternating layers of cobalt (Co) and permalloy (Fe20Ni80). We observe that the exchange magnons excited with energies lying in the energy gap die as soon as the Co layer gets wider.