Simon Pöllath, Tao Lin, Na Lei, Weisheng Zhao, Josef Zweck, Christian H. Back, "Spin structure relation to phase contrast imaging of isolated magnetic Bloch and Néel skyrmions", (Published 27.02.2020)
open access: arXiv:2002.12469
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 Néel 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 Néel skyrmions without the need of simulations. Furthermore, first differential phase contrast (DPC) measurements on Néel 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.
Katharina Zeissler, Simone Finizio, Craig Barton, Alexandra Huxtable, Jamie Massey, Jörg Raabe, Alexandr V. Sadovnikov, Sergey A. Nikitov, Richard Brearton, Thorsten Hesjedal, Gerrit van der Laan, Mark C. Rosamond, Edmund H. Linfield, Gavin Burnell and Christopher H. Marrows, "Diameter-independent skyrmion Hall angle in the plastic flow regime observed in chiral magnetic multilayers", (Published: 22.01.2020)
open access: arXiv:1908.04239
Magnetic skyrmions are topologically non-trivial nanoscale objects. Their topology, which originates in their chiral domain wall winding, governs their unique response to a motion-inducing force. When subjected to an electrical current, the chiral winding of the spin texture leads to a deflection of the skyrmion trajectory, characterized by an angle with respect to the applied force direction. This skyrmion Hall angle was believed to be skyrmion diameter-dependent. In contrast, our experimental study finds that within the plastic flow regime the skyrmion Hall angle is diameter-independent. At an average velocity of 6 ± 1 m/s the average skyrmion Hall angle was measured to be 9° ± 2°. In fact, in the plastic flow regime, the skyrmion dynamics is dominated by the local energy landscape such as materials defects and the local magnetic configuration.
Arianna Casiraghi, Héctor Corte-León, Mehran Vafaee, Felipe Garcia-Sanchez, Gianfranco Durin,Massimo Pasquale, Gerhard Jakob, Mathias Kläui and Olga Kazakova, "Individual skyrmion manipulation by local magnetic field gradients", Commun Phys 2, 145 (2019) (Published: 15.11.2019)
open access: arXiv:1903.00367
Magnetic skyrmions are topologically protected spin textures, stabilised in systems with strong Dzyaloshinskii-Moriya interaction (DMI). Several studies have shown that electrical currents can move skyrmions efficiently through spin-orbit torques. While promising for technological applications, current-driven skyrmion motion is intrinsically collective and accompanied by undesired heating effects. Here we demonstrate a new approach to control individual skyrmion positions precisely, which relies on the magnetic interaction between sample and a magnetic force microscopy (MFM) probe. We investigate perpendicularly magnetised X/CoFeB/MgO multilayers, where for X = W or Pt the DMI is sufficiently strong to allow for skyrmion nucleation in an applied field. We show that these skyrmions can be manipulated individually through the local field gradient generated by the scanning MFM probe with an unprecedented level of accuracy. Furthermore, we show that the probe stray field can assist skyrmion nucleation. Our proof-of-concepts results pave the way towards achieving current-free skyrmion control.
S. Saha, M. Zelent, S. Finizio, M. Mruczkiewicz, S. Tacchi, A. K. Suszka, S. Wintz, N. S. Bingham, J. Raabe, M. Krawczyk and L. J. Heyderman, "Formation of Néel-type skyrmions in an antidot lattice with perpendicular magnetic anisotropy", Phys. Rev. B 100, 144435 (Published: 25.10.2019)
open access: arXiv:1910.04515
Magnetic skyrmions are particlelike chiral spin textures found in magnetic films with out-of-plane anisotropy and are considered to be potential candidates as information carriers in next generation data storage devices. Despite intense research into the nature of skyrmions and their dynamic properties, there are several key challenges that still need to be addressed. In particular, the outstanding issues are the reproducible generation, stabilization, and confinement of skyrmions at room temperature. Here, we present a method for the capture of magnetic skyrmions in an array of defects in the form of an antidot lattice. We find that inhomogeneity in the total effective field produced by the antidot lattice is important for the formation of skyrmions which are mainly stabilized by the dipolar interaction. With micromagnetic simulations and scanning transmission x-ray microscopy we elucidate that the formation of skyrmions within the antidot lattice depends on the lattice constant and that, below a certain lattice constant, the skyrmion formation is suppressed. Based on our results we propose that, by varying the lattice constant, we can modify the probability of skyrmion formation in different parts of a sample by specific patterning. This provides another platform for experimental investigations of skyrmions and skyrmion-based devices.
Simon Pöllath, Aisha Aqeel, Andreas Bauer, Chen Luo, Hanjo Ryll, Florin Radu, Christian Pfleiderer, Georg Woltersdorf and Christian H. Back, "Ferromagnetic resonance with magnetic phase selectivity by means of resonant elastic x-ray scattering on a chiral magnet", Phys. Rev. Lett. 123, 167201 (Published: 14.10.2019)
open access: arXiv:1909.08293
Cubic chiral magnets, such as Cu2OSeO3, 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.
Simone Finizio, Katharina Zeissler, Sebastian Wintz, Sina Mayr, Teresa Weßels, Alexandra J. Huxtable, Gavin Burnell, Christopher H. Marrows and Jörg Raabe, "Deterministic Field-Free Skyrmion Nucleation at a Nanoengineered Injector Device", Nano Lett. 2019, 19, 10, 7246-7255 (Published: 17.09.2019)
open access: arXiv:1902.10435
Magnetic skyrmions are topological solitons promising for applications as encoders for digital information. A number of different skyrmion-based memory devices have been recently proposed. In order to demonstrate a viable skyrmion-based memory device, it is necessary to reliably and reproducibly nucleate, displace, detect, and delete the magnetic skyrmions, possibly in the absence of external applied magnetic fields, which would needlessly complicate the device design. While the skyrmion displacement and detection have both been thoroughly investigated, much less attention has been dedicated to the study of the skyrmion nucleation process and its sub-nanosecond dynamics. In this study, we investigate the nucleation of magnetic skyrmions from a dedicated nanoengineered injector, demonstrating the reliable magnetic skyrmion nucleation at the remnant state. The sub-nanosecond dynamics of the skyrmion nucleation process were also investigated, allowing us to shine light on the physical processes driving the nucleation.
Christian Back, Giovanni Carlotti, Arianna Casiraghi, Gianfranco Durin, Felipe Garcia-Sanchez, Michaela Kuepferling, Christopher Marrows, Gabriel Soaresand Silvia Tacchi, "Measuring Interfacial Dzyaloshinskii-Moriya Interaction: A Review", proceedings (Published: 05.09.2019)
Giovanni Carlotti, "Pushing down the lateral dimension of single and coupled magnetic dots to the nanometric scale: characteristics and evolution of the spin-wave eigenmodes", Applied Physics Review 6 (3) 031304 (2019). (Published: 08.2019)
open access: arXiv:1908.11098
Planar magnetic nanoelements, either single- or multilayered, are exploited in a variety of current or forthcoming spintronic and/or ICT devices, such as read heads, magnetic memory cells, spin-torque nano-oscillators, nanomagnetic logic circuits, magnonic crystals, and artificial spin-ices. The lateral dimensions of the elemental magnetic components have been squeezed down during the last decade to a few tens of nanometers, but they are still an order of magnitude larger than the exchange correlation length of the constituent materials. This means that the spectrum of spin-wave eigenmodes, occurring in the gigahertz range, is relatively complex and cannot be described within a simple macrospin approximation. On the other hand, a detailed knowledge of the dynamical spectrum is needed to understand or to predict crucial characteristics of the devices. With this focused review, we aim at the analysis and the rationalization of the characteristics of the eigenmode spectrum of magnetic nanodots, paying special attention to the following key points: (i) Consider and compare the case of in-plane and out of-plane orientation of the magnetization, as well as of single- and multilayered dots, putting in evidence similarities and diversities, and proposing a unifying nomenclature and labeling scheme; (ii) Underline the evolution of the spectrum when the lateral size of magnetic dots is squeezed down from hundreds to tens of nanometers, as in current devices, with emphasis given to the occurrence of soft modes and to the change of spatial localization of the fundamental mode for in-plane magnetized dots; (iii) Extend the analysis from isolated elements to twins of dots, as well as to dense arrays of dipolarly interacting dots, showing how the discretized eigenmodes distinctive of the single element transform in finite-width frequency bands of spin waves propagating through the array.
Katharina Zeissler, Simone Finizio, Craig Barton, Alexandra Huxtable, Jamie Massey, Jörg Raabe, Alexandr V. Sadovnikov, Sergey A. Nikitov, Richard Brearton, Thorsten Hesjedal, Gerrit van der Laan, Mark C. Rosamond, Edmund H. Linfield, Gavin Burnell and Christopher H. Marrows, "Dataset associated with 'Diameter-independent skyrmion Hall angle observed in chiral magnetic multilayers' ", University of Leeds OAR, (2019)
Simone Finizio, Katharina Zeissler, Sebastian Wintz, Sina Mayr, Teresa Weßels, Alexandra J. Huxtable, Gavin Burnell, Christopher H. Marrows and Jörg Raabe ,"Dataset associated with 'Deterministic Field-Free Skyrmion Nucleation at a Nanoengineered Injector Device' ", University of Leeds OAR, (2019)
Linked Publication: Simone Finizio et al., Nano Lett. 2019, 19, 10, 7246-7255
Arianna Casiraghi, Héctor Corte-León, Mehran Vafaee, Felipe Garcia-Sanchez, Gianfranco Durin,Massimo Pasquale, Gerhard Jakob, Mathias Kläui and Olga Kazakova, "Magnetic force microscopy data", Zenodo, (2019)
Linked Publication: Arianna Casiraghi et al., Commun Phys 2, 145 (2019)
Christian Back, "Ferromagnetic resonance data", Zenodo, (2019)
Linked Publication: Pöllath et al., Phys. Rev. Lett. 123, 167201