Research challenge 2: Skyrmion science

Research challenge 2: Skyrmion science

Research Challenge 2 concerns Skyrmion Science: the basic physics of skyrmionic states of matter. Before skyrmions can be exploited in devices it is necessary to understand their properties, potentialities and their status within the general framework of fundamental physics.

The skyrmion is a topological defect much like the magnetic domain wall and the superconducting vortex. If skyrmions can be made energetically stable they should occur within many systems showing broken symmetry and show a characteristic set of excitations.

How do skyrmion phases occur and what determines the form of the skyrmionic texture?

At one time, magnetic skyrmions were thought only to be realised in B20 magnetic systems. Recently it has become clear that a far richer variety of skyrmion textures may occur in a diverse range of systems. These textures include not only the Bloch-like skyrmion occurring in B20 chiral magnets but also the Neel-type skyrmion.

Stereographic projection (denoted P) squashes the hedgehog into D = 2, where it becomes a skyrmion. The left-hand version is a Néel skyrmion; the right-hand version, where the spins have been combed over (denoted R), is a Bloch skyrmion [8 - 2019 and references therein].

In bulk materials, the skyrmion lattice (SL) phase generally occurs within a narrow region of the applied magnetic field-temperature phase diagram. The reason for this, the nature of the phase transition, the possibility of precursor phases and the critical behavior on entering the skyrmion phase have all required detailed study.

The magnetic phase diagram of the (Cu1−xZnx)2OSeO3 sample, as determined by measurements of the electric polarisation P along the [001] crystallographic axis, when the magnetic field is applied along the [110] axis. The phase diagram was determined by field cooling (FC) at 20 mT, as indicated by the green arrow. The uniform magnetisation (UM, white), conical (C, blue), helical (H, red) and equilibrium skyrmion lattice (SkL, yellow) phases are labelled. The metastable SkL phase is divided into two regions, where it overlays the equilibrium conical (yellow hatched) and helical (yellow dotted) phases [1 - 2021].

How does dimensionality affect the skyrmion?

When bulk, crystalline samples are thinned the skyrmion phase becomes more stable, extending over a greater range of temperatures and applied magnetic fields. However, the observation of skyrmions in thin magnetic films has proved highly controversial, with no widely accepted observation of skyrmions in such films. The latter is of extreme importance since the manipulation of skyrmions in devices will most likely rely on magnetic thin-film technology. We have investigated the confinement of the SL along with the phase diagrams and spin textures realized in near-single layer samples and thin films.

Layer-dependent magnetic domain structures in on Fe5GeTe2. The images obtained for (a,b) 4 layer and 3 layer, and (c) 2 layer flakes show a strong dependence on thickness (T = 50 K). The distribution of up (red) and down (blue) domains for each thickness are indicated in (a) and (c). [6 - 2022].

How does the skyrmion evolve on different scales?

The skyrmion phase promotes a range of emergent physics. Using our suite of technique we have probed the excitations of the skyrmion phase on a number of length-, time- and energy-scales. There is also evidence that the extent of the SL phase is dependent on sample cooling rates, with quench-cooling stabilizing a larger skyrmion phase. Investigations of non-equilibrium effects have allowed us to stabilize these objects under a variety of conditions.

How robust is the skyrmion and the SL?

Little is known about the effects of disorder on the skyrmion phase. We have investigated the stability of skyrmion lattice and other related structures in bulk and thin film samples. We have examined the effects of confinement and dimensionality. We have also studied how introducing disorder, for example, by chemical doping alter the structure and stability of the skymion lattice.

REXS measurements on surface and bulk skyrmions in Cu2OSeO3. (a) Temperature-field phase diagram mapped by REXS. The dots represent measured data points. The skyrmion bulk state (SBS) region, defined by the characteristic REXS pattern as shown in Figure 1(f), is marked in red. The bulk phase boundary is consistent with the ac susceptibility measurements for both field-cooled and zero-field-cooled protocols. The skyrmion surface state (SSS) region is marked in yellow. (b) Magnetic phase diagram showing the ac susceptibility plot (real component χ′) obtained using the same protocol as for the REXS plot in (a), i.e., field cooling from above TC. (c, d) Reciprocal space maps of the surface state measured under surface-sensitive (931.2 eV) and bulk-sensitive (926.2 eV) conditions, respectively. (e) Illustration of the skyrmion surface state [20 -2020].

Experimental techniques

We have investigated phase transitions and skyrmion textures in a variety of materials using a broad range of experimental techniques and theoretical modelling.

Our starting point was to exploit the similarity between the skyrmion lattice (SL) and another topological defect state: the vortex lattice (VL) in type-II superconductors. This approach has allowed us to identify a powerful set of probes and tools for use in the project.

Neutron diffraction techniques have an advantage in examining large-scale magnetic structures such as SLs in that they produce data corresponding to the morphology of the field distribution in the bulk of a sample rather than a surface view provided by many methods.

(a) SANS H-T phase diagram of the Ni-substituted Cu2OSeO3, derived by summing the scattered neutron intensity in the region of the detector between the two white circles indicated in (b). The dashed lines identify the boundaries between the various magnetic phases in the sample. The solid white vertical line indicates the value of TC measured with ac susceptibility. (b) Typical skyrmion lattice scattering pattern recorded using SANS in Ni-substituted Cu2OSeO3 at 22 mT and 57 K [8 - 2020].

Transmission Electron Microscopy Magnetic imaging techniques (known collectively as Lorentz microscopy) are based on the fact that the Lorentz force from internal magnetic fields deflects electrons as they pass through a material, altering the phase of the electron wavefunction. We have used the technique to measure the magnetic profile of individual skyrmions and track magnetic phase transitions. Electron microscopy is the only imaging technique which gives information on the internal magnetic structure of the SL rather than just the stray field, and allows imaging at video rate.

LTEM images showing two skyrmion clusters (outlined in red) embedded in the cone phase of Cu2OSeO3 at 11 K in an out-of-plane applied magnetic field of μ0H = 116 mT. (b)–(d) show changes in the shape of the left-hand cluster with (c) taken 0.5 s and (d) taken 34.4 s after (b) [4 - 2018].

Using x-ray diffraction we have studied magnetic superlattice reflections such as magnetic spin density waves and antiferromagnetic and incommensurate reflections. We have used polarized soft x-ray diffraction, where we measure the polarization of the scattered x-rays to provide element-specific information on magnetic anisotropy.

Advanced imaging techniques including high-resolution ptychographic imaging have been used to examine skyrmions in bulk and thin film samples.

Ptychographic imaging is used to map the 2D spin texture of skyrmions in a Ta/[CoFeB/MgO/Ta]16 multilayer. The sample is raster-scanned while the focused X-ray beam remains fixed. The focusing of the beam is achieved by a Fresnel zone plate (FZP), where an order sorting aperture (OSA) blocks the nondiffracted zero-order light. A diffraction image is recorded in the far-field by a CCD camera (at distance L) for every scanning position. Applying an iterative phase retrieval algorithm allows for the reconstruction of the phase and amplitude images [9 - 2019].

Muon-spin rotation provides a means of accurately measuring the internal magnetic field distribution in a material through the implantation of spin-polarized muons. The technique hasused to provide key measurements of skymion dynamics, and we have shown that the technique allows an insight into the physics of the SL.

Typical muon spectroscopy time-domain spectra measured for GaV4S8 (left) and GaV4Se8 (right) in zero-field in the ferromagnetic (FM), cycloidal (C), and paramagnetic (PM) phases. Lines are fits described in the text and the curves have been offset vertically for clarity [2 -2018].

Theoretical methods and modelling:

Underpinning theoretical work will guide and allow us to understand our experimental results.

We have employed state-of-the-art multiscale theoretical and computational methods applicable in broad ranges of time, length and energy scales, and big data analysis tools, to understand the fundamental aspects of skyrmion physics. This work has involved first principles calculations, such as DFT, to identify the physics at play, and has been followed by modelling and calculations of static properties and excitations such as magnons and phonons. Techniques employed in this Challenge include: (i) lattice spin models and Monte-Carlo simulations to establish phase diagrams; (ii) Langevin spin dynamics simulations to probe skyrmion lifetimes and dynamics; (iii) micromagnetic simulations to model confinement effects and interactions with defects; (iv) micromagnetic, Monte-Carlo and large-scale spin dynamics simulations to model skyrmion interactions, long time-scale dynamics of the spin textures. Spin models were also used to compute the static and dynamic structure factors to directly support scattering experiments.

Three dimensional visualisation of three magnetic skyrmion tubes from micromagnetic simulations illustrating their extended spin structure. The inset highlights the location of the magnetic Bloch point at the end of each skyrmion tube [1 - 2020].


Publications

Please find below a list of papers published by the UK Skyrmion Project team as a results of work carried out during the course of the project under Research Challenges, 1, 2, and 3.

Some of the early papers are the result of pilot studies carried out my members of the UKSP team before the project was funded by the EPSRC.

Details of every publication, including an abstract and link to the paper in the journal can be found on the Journal section of this website under the heading Science.



Publications 2016


[1 - 2016] R. Carey, M. Beg, M. Albert, M.-A. Bisotti, D. Cortés-Ortuño, M. Vousden, W. Wang, O. Hovorka, H. Fangohr, Hysteresis of nanocylinders with Dzyaloshinskii-Moriya interaction, Applied Physics Letters 109, 122401 (2016).


[2 - 2016] A. I. Figueroa, S. L. Zhang, A. A. Baker, R. Chalasani, A. Kohn, S. C. Speller, D. Gianolio, C. Pfleiderer, G. van der Laan, T. Hesjedal, Strain in epitaxial MnSi films on Si(111) in the thick film limit studied by polarization-dependent extended x-ray absorption fine structure, Physical Review B 94, 174107 (2016).


[3 - 2016] V. P. Kravchuk, U. K. Rößler, O. M. Volkov, D. D. Sheka, J. van den Brink, D. Makarov, H. Fuchs, H. Fangohr, Y. Gaididei, Topologically stable magnetization states on a spherical shell: Curvature-stabilized skyrmions, Physical Review B 94, 144402 (2016).


[4 - 2016] T. Lancaster, R. C. Williams, I. O. Thomas, F. Xiao, F. L. Pratt, S. J. Blundell, J. C. Loudon, T. Hesjedal, S. J. Clark, P. D. Hatton, M. Ciomaga Hatnean, D. S. Keeble, G. Balakrishnan, Transverse field muon-spin rotation signature of the skyrmion-lattice phase in Cu2OSeO3, Physical Review B 91, 224408 (2015).


[5 - 2016] T. Lancaster, F. Xiao, Z. Salman, I. O. Thomas, S. J. Blundell, F. L. Pratt, S. J. Clark, T. Prokscha, A. Suter, S. L. Zhang, A. A. Baker, T. Hesjedal, Transverse field muon-spin rotation measurement of the topological anomaly in a thin film of MnSi, Physical Review B 93, 140412 (2016).


[6 - 2016] A. O. Leonov, J. C. Loudon, A. N. Bogdanov, Spintronics via non-axisymmetric chiral skyrmions, Applied Physics Letters 109, 172404 (2016).


[7 - 2016] A. O. Leonov, T. L. Monchesky, J. C. Loudon, A. N. Bogdanov, Three-dimensional chiral skyrmions with attractive interparticle interactions, Journal of Physics: Condensed Matter 28, 35LT01 (2016).


[8 - 2016] S. L. Zhang, A. Bauer, H. Berger, C. Pfleiderer, G. v. d. Laan, T. Hesjedal, Imaging and manipulation of skyrmion lattice domains in Cu2OSeO3, Applied Physics Letters 109, 192406 (2016).


[9 - 2016] S. L. Zhang, T. Hesjedal, The magneto-Hall difference and the planar extraordinary Hall balance, Aip Advances 6, 045019 (2016).




Publications 2017


[1 - 2017] A. Baker, M. Beg, G. Ashton, M. Albert, D. Chernyshenko, W. Wang, S. Zhang, M.-A. Bisotti, M. Franchin, C. L. Hu, R. Stamps, T. Hesjedal, H. Fangohr, Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations, Journal of Magnetism and Magnetic Materials 421, 428-439 (2017).


[2 - 2017] M. Beg, M. Albert, M.-A. Bisotti, D. Cortés-Ortuño, W. Wang, R. Carey, M. Vousden, O. Hovorka, C. Ciccarelli, C. S. Spencer, C. H. Marrows, H. Fangohr, Dynamics of skyrmionic states in confined helimagnetic nanostructures, Physical Review B 95, 014433 (2017).


[3 - 2017] D. Cortés-Ortuño, W. Wang, M. Beg, R. A. Pepper, M.-A. Bisotti, R. Carey, M. Vousden, T. Kluyver, O. Hovorka, H. Fangohr, Thermal stability and topological protection of skyrmions in nanotracks, Scientific Reports 7, 4060 (2017).


[4 - 2017] S. L. Zhang, I. Stasinopoulos, T. Lancaster, F. Xiao, A. Bauer, F. Rucker, A. A. Baker, A. I. Figueroa, Z. Salman, F. L. Pratt, S. J. Blundell, T. Prokscha, A. Suter, J. Waizner, M. Garst, D. Grundler, G. van der Laan, C. Pfleiderer, T. Hesjedal, Room-temperature helimagnetism in FeGe thin films, Scientific Reports 7, 123 (2017).


[5 - 2017] S. L. Zhang, G. van der Laan, T. Hesjedal, Direct experimental determination of the topological winding number of skyrmions in Cu2OSeO3, Nature Communications 8, 14619 (2017).


[6 - 2017] S. L. Zhang, G. van der Laan, T. Hesjedal, Direct experimental determination of spiral spin structures via the dichroism extinction effect in resonant elastic soft x-ray scattering, Physical Review B 96, 094401 (2017).




Publications 2018


[1 - 2018] D. Cortés-Ortuño, M. Beg, V. Nehruji, L. Breth, R. Pepper, T. Kluyver, G. Downing, T. Hesjedal, P. Hatton, T. Lancaster, R. Hertel, O. Hovorka, H. Fangohr, Proposal for a micromagnetic standard problem for materials with Dzyaloshinskii–Moriya interaction, New Journal of Physics 20, 113015 (2018).


[2 - 2018] K. J. A. Franke, B. M. Huddart, T. J. Hicken, F. Xiao, S. J. Blundell, F. L. Pratt, M. Crisanti, J. A. T. Barker, S. J. Clark, A. Štefančič, M. C. Hatnean, G. Balakrishnan, T. Lancaster, Magnetic phases of skyrmion-hosting GaV4S8-ySey (y=0,2,4,8) probed with muon spectroscopy, Physical Review B 98, 054428 (2018).


[3 - 2018] W. Jiang, J. Xia, X. Zhang, Y. Song, C. Ma, H. Fangohr, G. Zhao, X. Liu, W. Zhao, Y. Zhou, Dynamics of Magnetic Skyrmion Clusters Driven by Spin-Polarized Current With a Spatially Varied Polarization, IEEE Magnetics Letters 9, 1-5 (2018).


[4 - 2018] J. C. Loudon, A. O. Leonov, A. N. Bogdanov, M. C. Hatnean, G. Balakrishnan, Direct observation of attractive skyrmions and skyrmion clusters in the cubic helimagnet Cu2OSeO3, Physical Review B 97, 134403 (2018).


[5 - 2018] R. A. Pepper, M. Beg, D. Cortés-Ortuño, T. Kluyver, M.-A. Bisotti, R. Carey, M. Vousden, M. Albert, W. Wang, O. Hovorka, H. Fangohr, Skyrmion states in thin confined polygonal nanostructures, Journal of Applied Physics 123, 093903 (2018).


[6 - 2018] T. Shang, M. Smidman, S. K. Ghosh, C. Baines, L. J. Chang, D. J. Gawryluk, J. A. T. Barker, R. P. Singh, D. M. Paul, G. Balakrishnan, E. Pomjakushina, M. Shi, M. Medarde, A. D. Hillier, H. Q. Yuan, J. Quintanilla, J. Mesot, T. Shiroka, Time-Reversal Symmetry Breaking in Re-Based Superconductors, Physical Review Letters 121, 257002 (2018).


[7 - 2018] A. Štefančič, S. H. Moody, T. J. Hicken, M. T. Birch, G. Balakrishnan, S. A. Barnett, M. Crisanti, J. S. O. Evans, S. J. R. Holt, K. J. A. Franke, P. D. Hatton, B. M. Huddart, M. R. Lees, F. L. Pratt, C. C. Tang, M. N. Wilson, F. Xiao, T. Lancaster, Origin of skyrmion lattice phase splitting in Zn-substituted Cu2OSeO3, Physical Review Materials 2, 111402 (2018).


[8 - 2018] S. Zhang, F. Kronast, G. van der Laan, T. Hesjedal, Real-Space Observation of Skyrmionium in a Ferromagnet-Magnetic Topological Insulator Heterostructure, Nano Letters 18, 1057-1063 (2018).


[9 - 2018] S. Zhang, G. van der Laan, J. Müller, L. Heinen, M. Garst, A. Bauer, H. Berger, C. Pfleiderer, T. Hesjedal, Reciprocal space tomography of 3D skyrmion lattice order in a chiral magnet, Proceedings of the National Academy of Sciences 115, 6386-6391 (2018).


[10 - 2018] S. L. Zhang, G. van der Laan, W. W. Wang, A. A. Haghighirad, T. Hesjedal, Direct Observation of Twisted Surface skyrmions in Bulk Crystals, Physical Review Letters 120, 227202 (2018).


[11 - 2018] S. L. Zhang, W. W. Wang, D. M. Burn, H. Peng, H. Berger, A. Bauer, C. Pfleiderer, G. van der Laan, T. Hesjedal, Manipulation of skyrmion motion by magnetic field gradients, Nature Communications 9, 2115 (2018).




Publications 2019


[1 - 2019] M. T. Birch, R. Takagi, S. Seki, M. N. Wilson, F. Kagawa, A. Štefančič, G. Balakrishnan, R. Fan, P. Steadman, C. J. Ottley, M. Crisanti, R. Cubitt, T. Lancaster, Y. Tokura, P. D. Hatton, Increased lifetime of metastable skyrmions by controlled doping, Physical Review B 100, 014425 (2019).


[2 - 2019] R. Brearton, M. W. Olszewski, S. Zhang, M. R. Eskildsen, C. Reichhardt, C. J. O. Reichhardt, G. van der Laan, T. Hesjedal, Skyrmions in anisotropic magnetic fields: strain and defect driven dynamics, MRS Advances 4, 643-650 (2019).


[3 - 2019] D. M. Burn, S. L. Zhang, S. Wang, H. F. Du, G. van der Laan, T. Hesjedal, Helical magnetic ordering in thin FeGe membranes, Physical Review B 100, 184403 (2019).


[4 - 2019] D. Cortés-Ortuño, N. Romming, M. Beg, K. von Bergmann, A. Kubetzka, O. Hovorka, H. Fangohr, R. Wiesendanger, Nanoscale magnetic skyrmions and target states in confined geometries, Physical Review B 99, 214408 (2019).


[5 - 2019] K. J. A. Franke, P. R. Dean, M. C. Hatnean, M. T. Birch, D. D. Khalyavin, P. Manuel, T. Lancaster, G. Balakrishnan, P. D. Hatton, Investigating the magnetic ground state of the skyrmion host material Cu2OSeO3 using long-wavelength neutron diffraction, AIP Advances 9, 125228 (2019).


[6 - 2019] R. A. Gallardo, D. Cortés-Ortuño, T. Schneider, A. Roldán-Molina, F. Ma, R. E. Troncoso, K. Lenz, H. Fangohr, J. Lindner, P. Landeros, Flat Bands, Indirect Gaps, and Unconventional Spin-Wave Behavior Induced by a Periodic Dzyaloshinskii-Moriya Interaction, Physical Review Letters 122, 067204 (2019).


[7 - 2019] B. M. Huddart, M. T. Birch, F. L. Pratt, S. J. Blundell, D. G. Porter, S. J. Clark, W. Wu, S. R. Julian, P. D. Hatton, T. Lancaster, Local magnetism, magnetic order and spin freezing in the ‘nonmetallic metal’ FeCrAs, Journal of Physics: Condensed Matter 31, 285803 (2019).


[8 - 2019] T. Lancaster, Skyrmions in magnetic materials, Contemporary Physics 60, 246-261 (2019).


[9 - 2019] W. Li, I. Bykova, S. Zhang, G. Yu, R. Tomasello, M. Carpentieri, Y. Liu, Y. Guang, J. Gräfe, M. Weigand, D. M. Burn, G. van der Laan, T. Hesjedal, Z. Yan, J. Feng, C. Wan, J. Wei, X. Wang, X. Zhang, H. Xu, C. Guo, H. Wei, G. Finocchio, X. Han, G. Schütz, Anatomy of Skyrmionic Textures in Magnetic Multilayers, Advanced Materials 31, 1807683 (2019).


[10 - 2019] X. Li, S. Zhang, H. Li, D. A. Venero, J. S. White, R. Cubitt, Q. Huang, J. Chen, L. He, G. van der Laan, W. Wang, T. Hesjedal, F. Wang, Oriented 3D Magnetic Biskyrmions in MnNiGa Bulk Crystals, Advanced Materials 31, 1900264 (2019).


[11 - 2019] J. Liu, T. Hesjedal, Magnetic Topological Insulator Heterostructures: A Review, Advanced Materials n/a, 2102427


[12 - 2019] J. C. Loudon, A. C. Twitchett-Harrison, D. Cortés-Ortuño, M. T. Birch, L. A. Turnbull, A. Štefančič, F. Y. Ogrin, E. O. Burgos-Parra, N. Bukin, A. Laurenson, H. Popescu, M. Beg, O. Hovorka, H. Fangohr, P. A. Midgley, G. Balakrishnan, P. D. Hatton, Do Images of Biskyrmions Show Type-II Bubbles?, Advanced Materials 31, 1806598 (2019).


[13 - 2019] M. N. Wilson, M. Crisanti, C. Barker, A. Štefančič, J. S. White, M. T. Birch, G. Balakrishnan, R. Cubitt, P. D. Hatton, Measuring the formation energy barrier of skyrmions in zinc-substituted Cu2OSeO3, Physical Review B 99, 174421 (2019).


[14 - 2019] S. Zhang, T. Hesjedal, G. van der Laan, Skyrmions getting an X-ray, MagNews 2019, 22-22 (2020).




Publications 2020


[1 - 2020] M. T. Birch, D. Cortés-Ortuño, L. A. Turnbull, M. N. Wilson, F. Groß, N. Träger, A. Laurenson, N. Bukin, S. H. Moody, M. Weigand, G. Schütz, H. Popescu, R. Fan, P. Steadman, J. A. T. Verezhak, G. Balakrishnan, J. C. Loudon, A. C. Twitchett-Harrison, O. Hovorka, H. Fangohr, F. Y. Ogrin, J. Gräfe, P. D. Hatton, Real-space imaging of confined magnetic skyrmion tubes, Nature Communications 11, 1726 (2020).


[2 - 2020] M. T. Birch, S. H. Moody, M. N. Wilson, M. Crisanti, O. Bewley, A. Štefančič, G. Balakrishnan, R. Fan, P. Steadman, D. Alba Venero, R. Cubitt, P. D. Hatton, Anisotropy-induced depinning in the Zn-substituted skyrmion host Cu2OSeO3, Physical Review B 102, 104424 (2020).


[3 - 2020] R. Brearton, G. van der Laan, T. Hesjedal, Magnetic skyrmion interactions in the micromagnetic framework, Physical Review B 101, 134422 (2020).


[4 - 2020] D. M. Burn, S. Wang, W. Wang, G. van der Laan, S. Zhang, H. Du, T. Hesjedal, Field and temperature dependence of the skyrmion lattice phase in chiral magnet membranes, Physical Review B 101, 014446 (2020).


[5 - 2020] D. M. Burn, S. Zhang, K. Zhai, Y. Chai, Y. Sun, G. van der Laan, T. Hesjedal, Mode-Resolved Detection of Magnetization Dynamics Using X-ray Diffractive Ferromagnetic Resonance, Nano Letters 20, 345-352 (2020).


[6 - 2020] D. M. Burn, S. L. Zhang, G. Q. Yu, Y. Guang, H. J. Chen, X. P. Qiu, G. van der Laan, T. Hesjedal, Depth-Resolved Magnetization Dynamics Revealed by X-Ray Reflectometry Ferromagnetic Resonance, Physical Review Letters 125, 137201 (2020).


[7 - 2020] P. Chen, Y. Zhang, Q. Yao, F. Tian, L. Li, Z. Qi, X. Liu, L. Liao, C. Song, J. Wang, J. Xia, G. Li, D. M. Burn, G. van der Laan, T. Hesjedal, S. Zhang, X. Kou, Tailoring the Hybrid Anomalous Hall Response in Engineered Magnetic Topological Insulator Heterostructures, Nano Letters 20, 1731-1737 (2020).


[8 - 2020] M. Crisanti, M. T. Birch, M. N. Wilson, S. H. Moody, A. Štefančič, B. M. Huddart, S. Cabeza, G. Balakrishnan, P. D. Hatton, R. Cubitt, Position-dependent stability and lifetime of the skyrmion state in nickel-substituted Cu2OSeO3, Physical Review B 102, 224407 (2020).


[9 - 2020] M. Crisanti, N. Reynolds, I. Živković, A. Magrez, H. M. Rønnow, R. Cubitt, J. S. White, In situ control of the helical and skyrmion phases in Cu2OSeO3 using high-pressure helium gas up to 5 kbar, Physical Review B 101, 214435 (2020).


[10 - 2020] Y. Guang, Y. Peng, Z. Yan, Y. Liu, J. Zhang, X. Zeng, S. Zhang, S. Zhang, D. M. Burn, N. Jaouen, J. Wei, H. Xu, J. Feng, C. Fang, G. van der Laan, T. Hesjedal, B. Cui, X. Zhang, G. Yu, X. Han, Electron Beam Lithography of Magnetic Skyrmions, Advanced Materials 32, 2003003 (2020).


[11 - 2020] T. J. Hicken, S. J. R. Holt, K. J. A. Franke, Z. Hawkhead, A. Štefančič, M. N. Wilson, M. Gomilšek, B. M. Huddart, S. J. Clark, M. R. Lees, F. L. Pratt, S. J. Blundell, G. Balakrishnan, T. Lancaster, Magnetism and Néel skyrmion dynamics in GaV4S8-ySey, Physical Review Research 2, 032001 (2020).


[12 - 2020] S. J. R. Holt, A. Štefančič, C. Ritter, A. E. Hall, M. R. Lees, G. Balakrishnan, Structure and magnetism of the skyrmion hosting family GaV4S8-ySey with low levels of substitutions between 0 < y < 0.5 and 7.5 < y < 8, Physical Review Materials 4, 114413 (2020).


[13 - 2020] G. R. Lewis, J. C. Loudon, R. Tovey, Y.-H. Chen, A. P. Roberts, R. J. Harrison, P. A. Midgley, E. Ringe, Magnetic Vortex States in Toroidal Iron Oxide Nanoparticles: Combining Micromagnetics with Tomography, Nano Letters 20, 7405-7412 (2020).


[14 - 2020] J. Liu, A. Singh, B. Kuerbanjiang, C. H. W. Barnes, T. Hesjedal, Kerr effect anomaly in magnetic topological insulator superlattices, Nanotechnology 31, 434001 (2020).


[15 - 2020] J. Liu, A. Singh, Y. Y. F. Liu, A. Ionescu, B. Kuerbanjiang, C. H. W. Barnes, T. Hesjedal, Exchange Bias in Magnetic Topological Insulator Superlattices, Nano Letters 20, 5315-5322 (2020).


[16 - 2020] T. Moorsom, S. Alghamdi, S. Stansill, E. Poli, G. Teobaldi, M. Beg, H. Fangohr, M. Rogers, Z. Aslam, M. Ali, B. J. Hickey, O. Cespedes, pi-anisotropy: A nanocarbon route to hard magnetism, Physical Review B 101, 060408 (2020).


[17 - 2020] A. Štefančič, S. J. R. Holt, M. R. Lees, C. Ritter, M. J. Gutmann, T. Lancaster, G. Balakrishnan, Establishing magneto-structural relationships in the solid solutions of the skyrmion hosting family of materials: GaV4S8−ySey, Scientific Reports 10, 9813 (2020).


[18 - 2020] M. N. Wilson, M. T. Birch, A. Štefančič, A. C. Twitchett-Harrison, G. Balakrishnan, T. J. Hicken, R. Fan, P. Steadman, P. D. Hatton, Stability and metastability of skyrmions in thin lamellae of Cu2OSeO3, Physical Review Research 2, 013096 (2020).


[19 - 2020] K. Zeissler, S. Finizio, C. Barton, A. J. Huxtable, J. Massey, J. Raabe, A. V. Sadovnikov, S. A. Nikitov, R. Brearton, T. Hesjedal, G. van der Laan, M. C. Rosamond, E. H. Linfield, G. Burnell, C. H. Marrows, Diameter-independent skyrmion Hall angle observed in chiral magnetic multilayers, Nature Communications 11, 428 (2020).


[20 - 2020] S. Zhang, D. M. Burn, N. Jaouen, J.-Y. Chauleau, A. A. Haghighirad, Y. Liu, W. Wang, G. van der Laan, T. Hesjedal, Robust Perpendicular Skyrmions and Their Surface Confinement, Nano Letters 20, 1428-1432 (2020).




Publications 2021


[1 - 2021] M. T. Birch, D. Cortés-Ortuño, N. D. Khanh, S. Seki, A. Štefančič, G. Balakrishnan, Y. Tokura, P. D. Hatton, Topological defect-mediated skyrmion annihilation in three dimensions, Communications Physics 4, 175 (2021).


[2 - 2021] R. Brearton, L. A. Turnbull, J. A. T. Verezhak, G. Balakrishnan, P. D. Hatton, G. van der Laan, T. Hesjedal, Deriving the skyrmion Hall angle from skyrmion lattice dynamics, Nature Communications 12, 2723 (2021).


[3 - 2021] D. M. Burn, R. Brearton, K. J. Ran, S. L. Zhang, G. van der Laan, T. Hesjedal, Periodically modulated skyrmion strings in Cu2OSeO3, npj Quantum Materials 6, 73 (2021).


[4 - 2021] D. M. Burn, S. L. Zhang, G. v. d. Laan, T. Hesjedal, Magnetization dynamics in ordered spin structures revealed by diffractive and reflectometry ferromagnetic resonance, AIP Advances 11, 015327 (2021).


[5 - 2021] S. P. M. Curley, B. M. Huddart, D. Kamenskyi, M. J. Coak, R. C. Williams, S. Ghannadzadeh, A. Schneider, S. Okubo, T. Sakurai, H. Ohta, J. P. Tidey, D. Graf, S. J. Clark, S. J. Blundell, F. L. Pratt, M. T. F. Telling, T. Lancaster, J. L. Manson, P. A. Goddard, Anomalous magnetic exchange in a dimerized quantum magnet composed of unlike spin species, Physical Review B 104, 214435 (2021).


[6 - 2021] A. E. Hall, D. D. Khalyavin, P. Manuel, D. A. Mayoh, F. Orlandi, O. A. Petrenko, M. R. Lees, G. Balakrishnan, Magnetic structure investigation of the intercalated transition metal dichalcogenide V1/3NbS2, Physical Review B 103, 174431 (2021).


[7 - 2021] T. J. Hicken, M. N. Wilson, K. J. A. Franke, B. M. Huddart, Z. Hawkhead, M. Gomilšek, S. J. Clark, F. L. Pratt, A. Štefančič, A. E. Hall, M. Ciomaga Hatnean, G. Balakrishnan, T. Lancaster, Megahertz dynamics in skyrmion systems probed with muon-spin relaxation, Physical Review B 103, 024428 (2021).


[8 - 2021] S. J. R. Holt, C. Ritter, M. R. Lees, G. Balakrishnan, Investigation of the magnetic ground state of GaV4S8 using powder neutron diffraction, Journal of Physics: Condensed Matter 33, 255802 (2021).


[9 - 2021] S. J. R. Holt, A. Štefančič, J. C. Loudon, M. R. Lees, G. Balakrishnan, Investigations of the size distribution and magnetic properties of nanoparticles of Cu2OSeO3, Materials Research Express 8, 116101 (2021).


[10 - 2021] B. M. Huddart, M. Gomilšek, T. J. Hicken, F. L. Pratt, S. J. Blundell, P. A. Goddard, S. J. Kaech, J. L. Manson, T. Lancaster, Magnetic order and ballistic spin transport in a sine-Gordon spin chain, Physical Review B 103, L060405 (2021).


[11 - 2021] G. v. d. Laan, S. L. Zhang, T. Hesjedal, Depth profiling of 3D skyrmion lattices in a chiral magnet—A story with a twist, AIP Advances 11, 015108 (2021).


[12 - 2021] S. Mañas-Valero, B. M. Huddart, T. Lancaster, E. Coronado, F. L. Pratt, Quantum phases and spin liquid properties of 1T-TaS2, npj Quantum Materials 6, 69 (2021).


[13 - 2021] D. A. Mayoh, G. D. A. Wood, S. J. R. Holt, G. Beckett, E. J. L. Dekker, M. R. Lees, G. Balakrishnan, Effects of Fe Deficiency and Co Substitution in Polycrystalline and Single Crystals of Fe3GeTe2, Crystal Growth & Design 21, 6786-6792 (2021).


[14 - 2021] S. H. Moody, P. Nielsen, M. N. Wilson, D. A. Venero, A. Štefančič, G. Balakrishnan, P. D. Hatton, Experimental evidence of a change of exchange anisotropy sign with temperature in Zn-substituted Cu2OSeO3, Physical Review Research 3, 043149 (2021).


[15 - 2021] K. Ran, Y. Liu, Y. Guang, D. M. Burn, G. van der Laan, T. Hesjedal, H. Du, G. Yu, S. Zhang, Creation of a Chiral Bobber Lattice in Helimagnet-Multilayer Heterostructures, Physical Review Letters 126, 017204 (2021).


[16 - 2021] L. A. Turnbull, M. T. Birch, A. Laurenson, N. Bukin, E. O. Burgos-Parra, H. Popescu, M. N. Wilson, A. Stefančič, G. Balakrishnan, F. Y. Ogrin, P. D. Hatton, Tilted X-Ray Holography of Magnetic Bubbles in MnNiGa Lamellae, ACS Nano 15, 387-395 (2021).


[17 - 2021] M. N. Wilson, T. J. Hicken, M. Gomilšek, A. Štefančič, G. Balakrishnan, J. C. Loudon, A. C. Twitchett-Harrison, F. L. Pratt, M. Telling, T. Lancaster, Spin dynamics in bulk MnNiGa and Mn1.4Pt0.9Pd0.1Sn investigated by muon spin relaxation, Physical Review B 104, 134414 (2021).


[18 - 2021] T. B. Winkler, K. Litzius, A. de Lucia, M. Weißenhofer, H. Fangohr, M. Kläui, Skyrmion States in Disk Geometry, Physical Review Applied 16, 044014 (2021).




Publications 2022


[1 - 2022] B. Achinuq, R. Fujita, W. Xia, Y. Guo, P. Bencok, G. van der Laan, T. Hesjedal, Covalent Mixing in the 2D Ferromagnet CrSiTe3 Evidenced by Magnetic X-Ray Circular Dichroism, Physica Status Solidi (RRL) – Rapid Research Letters 16, 2100566 (2022).

[2 - 2022] G. Awana, R. Fujita, A. Frisk, P. Chen, Q. Yao, A. J. Caruana, C. J. Kinane, N. J. Steinke, S. Langridge, P. Olalde-Velasco, S. S. Dhesi, G. van der Laan, X. F. Kou, S. L. Zhang, T. Hesjedal, D. Backes, Critical analysis of proximity-induced magnetism in MnTe/Bi2Te3 heterostructures, Physical Review Materials 6, 053402 (2022).

[3 - 2022] M. Beg, M. Lang, H. Fangohr, Ubermag: Toward More Effective Micromagnetic Workflows, IEEE Transactions on Magnetics 58, 7300205 (2022).

[4 - 2022] M. T. Birch, D. Cortés-Ortuño, K. Litzius, S. Wintz, F. Schulz, M. Weigand, A. Štefančič, D. A. Mayoh, G. Balakrishnan, P. D. Hatton, G. Schütz, Toggle-like current-induced Bloch point dynamics of 3D skyrmion strings in a room temperature nanowire, Nature Communications 13, 3630 (2022).

[5 - 2022] M. T. Birch, L. Powalla, S. Wintz, O. Hovorka, K. Litzius, J. C. Loudon, L. A. Turnbull, V. Nehruji, K. Son, C. Bubeck, T. G. Rauch, M. Weigand, E. Goering, M. Burghard, G. Schütz, History-dependent domain and skyrmion formation in 2D van der Waals magnet Fe3GeTe2, Nature Communications 13, 3035 (2022).

[6 - 2022] R. Fujita, P. Bassirian, Z. Li, Y. Guo, M. A. Mawass, F. Kronast, G. van der Laan, T. Hesjedal, Layer-Dependent Magnetic Domains in Atomically Thin Fe5GeTe2, ACS Nano 16, 10545-10553 (2022).

[7 - 2022] R. Fujita, J. Liu, X. Hou, Y. Guo, J. Herrero-Martín, G. van der Laan, T. Hesjedal, X-ray spectroscopy for the magnetic study of the van der Waals ferromagnet CrSiTe3 in the few- and monolayer limit, 2d Materials 9, 045007 (2022).

[8 - 2022] A. E. Hall, J. C. Loudon, P. A. Midgley, A. C. Twitchett-Harrison, S. J. R. Holt, D. A. Mayoh, J. P. Tidey, Y. Han, M. R. Lees, G. Balakrishnan, Comparative study of the structural and magnetic properties of Mn1/3NbS2 and Cr1/3NbS2, Physical Review Materials 6, 024407 (2022).

[9 - 2022] T. J. Hicken, Z. Hawkhead, M. N. Wilson, B. M. Huddart, A. E. Hall, G. Balakrishnan, C. Wang, F. L. Pratt, S. J. Clark, T. Lancaster, Energy-gap driven low-temperature magnetic and transport properties in Cr1/3MS2 (M = Nb, Ta), Physical Review B 105, L060407 (2022).

[10 - 2022] T. J. Hicken, M. N. Wilson, S. J. R. Holt, R. Khassanov, M. R. Lees, R. Gupta, D. Das, G. Balakrishnan, T. Lancaster, Magnetism in the N\'eel-skyrmion host GaV4S8 under pressure, Physical Review B 105, 134414 (2022).

[11 - 2022] D. A. Mayoh, J. Bouaziz, A. E. Hall, J. B. Staunton, M. R. Lees, G. Balakrishnan, Giant topological and planar Hall effect in Cr1/3NbS2, Physical Review Research 4, 013134 (2022).

[12 - 2022] K. Ran, Y. Liu, H. Jin, Y. Shangguan, Y. Guang, J. Wen, G. Yu, G. van der Laan, T. Hesjedal, S. Zhang, Axially Bound Magnetic Skyrmions: Glueing Topological Strings Across an Interface, Nano Letters 22, 3737-3743 (2022).

[13 - 2022] L. A. Turnbull, M. T. Littlehales, M. N. Wilson, M. T. Birch, H. Popescu, N. Jaouen, J. A. T. Verezhak, G. Balakrishnan, P. D. Hatton, X-ray holographic imaging of magnetic surface spirals in FeGe lamellae, Physical Review B 106, 064422 (2022).

[14 - 2022] A. C. Twitchett-Harrison, J. C. Loudon, R. A. Pepper, M. T. Birch, H. Fangohr, P. A. Midgley, G. Balakrishnan, P. D. Hatton, Confinement of Skyrmions in Nanoscale FeGe Device-like Structures, ACS Applied Electronic Materials DOI 10.1021/acsaelm.2c00692 (2022).