arXiv subjects

Simon Pöllath

Publications and source records attributed to Simon Pöllath.

3 recordsLinked to original sources

arXiv2020

Spin structure relation to phase contrast imaging of isolated magnetic Bloch and Neel skyrmions

Magnetic skyrmions are promising candidates for future storage devices with a large data density. A great variety of materials have been found that host skyrmions up to the room-temperature regime. Lorentz microscopy, usually performed in a transmission electron microscope (TEM), is one of the most important tools for characterizing skyrmion samples in real space. Using numerical calculations, this work relates the phase contrast in a TEM to the actual magnetization profile of an isolated Neel or Bloch skyrmion, the two most common skyrmion types. Within the framework of the used skyrmion model, the results are independent of skyrmion size and wall width and scale with sample thickness for purely magnetic specimens. Simple rules are provided to extract the actual skyrmion configuration of pure Bloch or Neel skyrmions without the need of simulations. Furthermore, first differential phase contrast (DPC) measurements on Neel skyrmions that meet experimental expectations are presented and showcase the described principles. The work is relevant for material sciences where it enables the engineering of skyrmion profiles via convenient characterization.

cond-mat.mes-hall↗

arXiv2019

Ferromagnetic resonance with magnetic phase selectivity by means of resonant elastic x-ray scattering on a chiral magnet

Cubic chiral magnets, such as Cu$_{2}$OSeO$_{3}$, exhibit a variety of non-collinear spin textures, including a trigonal lattice of spin whirls, so-called skyrmions. Using magnetic resonant elastic x-ray scattering (REXS) on a crystalline Bragg peak and its magnetic satellites while exciting the sample with magnetic fields at GHz frequencies, we probe the ferromagnetic resonance modes of these spin textures by means of the scattered intensity. Most notably, the three eigenmodes of the skyrmion lattice are detected with large sensitivity. As this novel technique, which we label REXS-FMR, is carried out at distinct positions in reciprocal space, it allows to distinguish contributions originating from different magnetic states, providing information on the precise character, weight and mode mixing as a prerequisite of tailored excitations for applications.

cond-mat.mtrl-sci↗

arXiv2019

Magnetic and electrical transport signatures of uncompensated moments in epitaxial thin films of the non-collinear antiferromagnet Mn$_{3}$Ir

Non-collinear antiferromagnets, with either an L1$_{2}$ cubic crystal lattice (e.g. Mn$_{3}$Ir and Mn$_{3}$Pt) or a D0$_{19}$ hexagonal structure (e.g. Mn$_{3}$Sn and Mn$_{3}$Ge), exhibit a number of novel phenomena of interest to topological spintronics. Amongst the cubic systems, for example, tetragonally distorted Mn$_{3}$Pt exhibits an intrinsic anomalous Hall effect (AHE). However, Mn$_{3}$Pt only enters a non-collinear magnetic phase close to the stoichiometric composition and at suitably large thicknesses. Therefore, we turn our attention to Mn$_{3}$Ir, the material of choice for use in exchange bias heterostructures. In this paper, we investigate the magnetic and electrical transport properties of epitaxially grown, face-centered-cubic $γ$-Mn$_{3}$Ir thin films with (111) crystal orientation. Relaxed films of 10 nm thickness exhibit an ordinary Hall effect, with a hole-type carrier concentration of (2.24 $\pm$ 0.08) $\times$ 10$^{23}$ cm$^{-3}$. On the other hand, TEM characterization demonstrates that ultrathin 3 nm films grow with significant in-plane tensile strain. This may explain a small remanent moment, observed at low temperatures, shown by XMCD spectroscopy to arise from uncompensated Mn spins. Of the order 0.02 $μ_{B}$ / atom, this dominates electrical transport behavior, leading to a small AHE and negative magnetoresistance. These results are discussed in terms of crystal microstructure and chiral domain behavior, with spatially resolved XML(C)D-PEEM supporting the conclusion that small antiferromagnetic domains, < 20 nm in size, of differing chirality account for the absence of observed Berry curvature driven magnetotransport effects.

cond-mat.mtrl-sci↗