Suchergebnisse

This project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 101001290). A.H.-R. and S.M. acknowledge support from the European Union's Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant H2020-MSCA-IF-2016-746958. A.H.-R. acknowledges funding from the Spanish AEI under project PID2019–104604RB/ AEI/10.13039/501100011033 ; Donnelly, C; Hierro-Rodriguez, A; Abert, C; Witte, K; Skoric, L; Sanz-Hernandez, D; Finizio, S; Meng, FF; McVitie, S; Raabe, J; Suess, D; Cowburn, R; Fernandez-Pacheco, A

[EN] Static magnetization configurations of thin soft ferromagnetic films and nanodots, coupled to a hard antidot matrix with out-of-plane magnetization, are studied by micromagnetic simulations and analytical calculations. When the antidot matrix produces sufficient stray fields, having radial symmetry, these nanostructures support the formation of topologically nontrivial magnetic configurations-vortices and skyrmions in nanodots and films, respectively. It is demonstrated that the studied nanostructure reveals an additional degree of freedom-the helicity of the vortex or skyrmion-which can be tuned on demand by a variation of the material parameters and geometry. The variation of helicity γ is not abrupt. In addition to Neel-like (radial) vortices and skyrmions (γ=0,π), it is possible to achieve unconventional configurations with an intermediate helicity γ≠0,±π/2,π, which transform to common Bloch-like configurations (γ=±π/2) in the limit of negligible stray fields from the matrix. We present an analytical model, which allows us to calculate the stability region of pure Neel-like states, outside which unconventional magnetization states with intermediate helicity are realized. ; The Portuguese team acknowledges the Network of Extreme Conditions Laboratories and Portuguese Foundation of Science and Technology for support through Projects No. NORTE-01-0145-FEDER-022096, No. MIT-EXPL/IRA/0012/2017, No. PTDC/FISMAC/31302/2017, No. POCI-0145-FEDER-030085(NOVAMAG), No. PTDC/FIS-MAC/31302/2017, andNo. EXPL/IF/00541/2015 (S.A.B.) and Grant No.SFRH/BPD/90471/2012 (A.H.-R.). Work was also supported by the Ministry of Education and Science of Ukraine, Project No. 0118U004007 (R.V.V., B.A.I.); IKERBASQUE (the Basque Foundation for Science) (K.Y.G.); the Spanish Ministry of Economy, Industry and Competitiveness, Grant No. FIS2016-78591-C3-3-R (K.Y.G.); the European Union Horizon 2020 Research and Innovation Programme under Marie Skłodowska-Curie Grants No. 644348 (R.V.V., B.A.I., K.Y.G.), No. H2020-MSCA-RISE-2016-734801 (D.N., G.N.K.), and No. H2020-MSCA-IF-2016-74695 (A.H.-R.); the Program of NUST "MISiS," Grant No. K2-2019-006, implemented by Russian Federation government Decree No. 211 dated 16 March 2013 (B.A.I.); the Spanish Ministry for Science, Innovation and Universities, for funding through the "Ramón y Cajal" Program No. RYC-2017-22820 (D.N.); and European Cooperation in Science and Technology, Projects No. CA16218 "NANOCOHYBRI" (G.N.K.) and No. CA17123 "MAGNETOFON" (B.A.I).

Magnetic lateral multilayers have been fabricated on weak perpendicular magnetic anisotropy amorphous Nd-Co films in order to perform a systematic study on the conditions for controlled nucleation of topological defects within their magnetic stripe domain pattern. A lateral thickness modulation of period w is defined on the nanostructured samples that, in turn, induces a lateral modulation of both magnetic stripe domain periods λ and average in-plane magnetization component Min-plane. Depending on lateral multilayer period and in-plane applied field, thin and thick regions switch independently during in-plane magnetization reversal and domain walls are created within the in-plane magnetization configuration coupled to variable angle grain boundaries and disclinations within the magnetic stripe domain patterns. This process is mainly driven by the competition between rotatable anisotropy (that couples the magnetic stripe pattern to in-plane magnetization) and in-plane shape anisotropy induced by the periodic thickness modulation. However, as the structural period w becomes comparable to magnetic stripe period λ, the nucleation of topological defects at the interfaces between thin and thick regions is hindered by a size effect and stripe domains in the different thickness regions become strongly coupled. © 2013 American Physical Society. ; Work was supported by Spanish MICINN under Grant No. FIS2008-06249. R.M. and N.S. acknowledge support from UPV/EHU UFI11/23 and Basque Country Government Grant No. Etorek SE11-304. A.H.-R. acknowledges support from FCT of Portugal grant (Grant No. SFRH/BPD/90471/2012). ; Peer Reviewed

The Portuguese team acknowledges the Network of Extreme Conditions Laboratories and Portuguese Foundation of Science and Technology for support through Projects No. NORTE-01-0145-FEDER-022096, No. MIT-EXPL/IRA/0012/2017, No. PTDC/FISMAC/31302/2017, No. POCI-0145-FEDER-030085 (NOVAMAG), No. PTDC/FIS-MAC/31302/2017, and No. EXPL/IF/00541/2015 (S.A.B.) and Grant No. SFRH/BPD/90471/2012 (A.H.-R.). Work was also supported by the Ministry of Education and Science of Ukraine, Project No. 0118U004007 (R.V.V., B.A.I.); IKERBASQUE (the Basque Foundation for Science) (K.Y.G.); the Spanish Ministry of Economy, Industry and Competitiveness, Grant No. FIS2016-78591-C3-3-R (K.Y.G.); the European Union Horizon 2020 Research and Innovation Programme under Marie Skłodowska-Curie Grants No. 644348 (R.V.V., B.A.I., K.Y.G.), No. H2020-MSCA-RISE-2016-734801 (D.N., G.N.K.), and No. H2020-MSCA-IF-2016-74695 (A.H.-R.); the Program of NUST "MISiS," Grant No. K2-2019-006, implemented by Russian Federation government Decree No. 211 dated 16 March 2013 (B.A.I.); the Spanish Ministry for Science, Innovation and Universities, for funding through the "Ramón y Cajal" Program No. RYC-2017-22820 (D.N.); and European Cooperation in Science and Technology, Projects No. CA16218 "NANOCOHYBRI" (G.N.K.) and No. CA17123 "MAGNETOFON" (B.A.I).

A.H.-R. acknowledges the support from European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant ref. H2020-MSCA-IF-2016-746958. ; Kent, N., Reynolds, N., Raftrey, D., Campbell, I.T.G., Virasawmy, S., Dhuey, S., Chopdekar, R.V., Hierro-Rodriguez, A., Sorrentino, A., Pereiro, E., Ferrer, S., Hellman, F., Sutcliffe, P., Fischer, P.

This article belongs to the Special Issue Recent Advances in Nanomagnetism. ; Ferromagnetic resonance is a powerful method for the study of all classes of magnetic materials. The experimental technique has been used for many decades and is based on the excitation of a magnetic spin system via a microwave (or rf) field. While earlier methods were based on the use of a microwave spectrometer, more recent developments have seen the widespread use of the vector network analyzer (VNA), which provides a more versatile measurement system at almost comparable sensitivity. While the former is based on a fixed frequency of excitation, the VNA enables frequency-dependent measurements, allowing more in-depth analysis. We have applied this technique to the study of nanostructured thin films or nanodots and coupled magnetic layer systems comprised of exchange-coupled ferromagnetic layers with in-plane and perpendicular magnetic anisotropies. In the first system, we have investigated the magnetization dynamics in Co/Ag bilayers and nanodots. In the second system, we have studied Permalloy (Ni80Fe20, hereafter Py) thin films coupled via an intervening Al layer of varying thickness to a NdCo film which has perpendicular magnetic anisotropy. ; D.S.S., D.M. and L.M.Á.-P. acknowledge financial support from the Institut de Physique of CNRS for experimental equipment, a post doc position, and guest researcher stays, respectively. A.H.-R. acknowledges European Union's Horizon 2020 framework program for research and innovation under the Marie Skłodowska-Curie Action No. H2020-MSCA-IF-2016-746958. A.H.-R., C.Q., J.D. and L.M.Á.-P. would like to thank the Spanish Ministerio de Ciencia e Innovación (MCI) for financial support under Project PID2019-104604RB/AEI/10.13039/501100011033. ; Peer reviewed

Resumen del trabajo presentado al American Physical Society March Meeting, celebrado on-line del 15 al 19 de marzo de 2021. ; Work supported by Spanish MINECO (Grants FIS2016-76058 (AEI/FEDER, EU) and PID2019-104604RB/AEI/10.13039/501100011033) and European Union's Horizon 2020 Marie Sklodowska-Curie Grant ref. H2020-MSCA-IF-2016-746958. ; Peer reviewed

The knowledge of how magnetization looks inside a ferromagnet is often hindered by the limitations of the available experimental methods which are sensitive only to the surface regions or limited in spatial resolution. Here we report a vector tomographic reconstruction based on soft X-ray transmission microscopy and magnetic dichroism data, which has allowed visualizing the three-dimensional magnetization in a ferromagnetic thin film heterostructure. Different non-trivial topological textures have been resolved and the determination of their topological charge has allowed us to identify a Bloch point and a meron-like texture. Our method relies only on experimental data and might be of wide application and interest in 3D nanomagnetism. ; Alba light source is funded by the Ministry of Research and Innovation of Spain and by the Generalitat de Catalunya and by European FEDER funds. This project has been supported by Spanish MINECO under grant FIS2016-76058 (AEI/FEDER, EU) and grant PID2019-104604RB/AEI/10.13039/501100011033. A.H.-R. and S.MV. acknowledge the support from European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant ref. H2020-MSCA-IF-2016-746958. ; Peer reviewed

The magnetization reversal of each individual layer in magnetic trilayers (permalloy/NdCo/GdCo) is investigated in detail with x-ray microscopy and micromagnetic calculations. Two sequential inversion mechanisms are identified. First, magnetic vortex-antivortex pairs move along the field direction while inverting the magnetization of magnetic stripes until they are pinned by defects. The vortex-antivortex displacements are reversible within a field interval which allows their controlled motion. Second, as the reversed magnetic field increases, cycloidal domains appear in the permalloy layer as a consequence of the dissociation of vortex-antivortex pairs due to pinning. The field range where magnetic vortices and antivortices are effectively guided by the stripe pattern is of the order of tens of mT for the NiFe layer, as estimated from the stability of cycloid domains in the sample. ; Work supported by Spanish MINECO [Grants No. FIS 2013-45469 and No. FIS2016-76058 (AEI/FEDER,EU)] and by FICYT-Asturias (Grant No. FC-GRUPIN14-040). We thank J. Avila (Alba staff) for assistance in the pulsed magnetic field set up. We thank Unidad de Medidas magnéticas y RMN de Sólidos de los Servicios Cientifico Técnicos of Universidad de Oviedo for the VSM characterization. A.H.-R. acknowledges the support from European Union's Horizon 2020 research and innovation programme under Marie Skłodowska-Curie Grant No. H2020-MSCAIF-2016-746958. ; Peer Reviewed

The development of magnetic nanostructures for applications in spintronics requires methods capable of visualizing their magnetization. Soft X-ray magnetic imaging combined with circular magnetic dichroism allows nanostructures up to 100–300 nm in thickness to be probed with resolutions of 20–40 nm. Here a new iterative tomographic reconstruction method to extract the three-dimensional magnetization configuration from tomographic projections is presented. The vector field is reconstructed by using a modified algebraic reconstruction approach based on solving a set of linear equations in an iterative manner. The application of this method is illustrated with two examples (magnetic nano-disc and micro-square heterostructure) along with comparison of error in reconstructions, and convergence of the algorithm. ; The following funding is acknowledged: Spanish MINECO (grant No. FIS2013-45469; grant No. FIS2016-76058 (AEI/FEDER, EU); contract No. FIS2016-76058 (AEI/FEDER, EU) to AHR); FICYT-Asturias (grant No. FC-GRUPIN14-040); US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory (contract No. DE-AC02-06CH11357 to DG); US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division (contract to CP). AHR acknowledges support from European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Action (reference H2020-MSCA-IF-2016-746958). ; Peer Reviewed

The design of complex, competing effects in magnetic systems – be it via the introduction of nonlinear interactions, or the patterning of three-dimensional geometries – is an emerging route to achieve new functionalities. Here, we combine 3D geometric effects with non-linear and non-local interactions to produce magnetic field textures in free space. For this, we harness direct write nanofabrication techniques, creating intertwined nanomagnetic cobalt double helices, where curvature, torsion, chirality, and magnetic coupling are jointly exploited. By reconstructing the 3D vectorial magnetic state of the double helices with soft X-ray magnetic laminography, we identify the presence of a regular array of highly coupled locked domain wall pairs in neighbouring helices. Micromagnetic simulations reveal that the magnetisation configuration leads to the formation of an array of complex textures in the magnetic induction, consisting of vortices in the magnetisation and antivortices in free space, which together, form an effective B-field cross-tie wall. The design and creation of complex three-dimensional magnetic field nanotextures opens new possibilities for smart materials, unconventional computing, particle trapping and magnetic imaging. ; This work was funded by an EPSRC Early Career Fellowship EP/M008517/1 and the Winton Program for the Physics of Sustainability. C.D. acknowledges funding from the Leverhulme Trust (ECF-2018-016), the Isaac Newton Trust (18-08), the L'Oréal-UNESCO UK and Ireland Fellowship For Women In Science 2019, and the Max Planck Society Lise Meitner Excellence Program. A.F.P. acknowledges funding by the European Community under the Horizon 2020 Program, Contract no. 101001290, 3DNANOMAG. A.H.-R. and S.MV. acknowledge the support from European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant ref. H2020-MSCA-IF-2016-746958. A.H.-R. acknowledges funding from Spanish AEI under project reference PID2019–104604RB/AEI/10.13039/501100011033. The PolLux end station was financed by the German Ministerium für Bildung und Forschung (BMBF) through contracts 05K16WED and 05K19WE2. K.W. acknowledges the funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 701647. A.F.P. is grateful to the University of Cambridge and the University of Glasgow, where part of this research was performed. ; Peer reviewed

This project has been supported by Spanish MINECO under grant FIS2016-76058 (AEI/FEDER, EU) and grant PID2019-104604RB/AEI/10.13039/501100011033. A.H.-R. and S.MV. acknowledge the support from European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant ref. H2020-MSCA-IF-2016-746958.

Chirality plays a major role in nature, from particle physics to DNA, and its control is much sought-after due to the scientific and technological opportunities it unlocks. For magnetic materials, chiral interactions between spins promote the formation of sophisticated swirling magnetic states such as skyrmions, with rich topological properties and great potential for future technologies. Currently, chiral magnetism requires either a restricted group of natural materials or synthetic thin-film systems that exploit interfacial effects. Here, using state-of-the-art nanofabrication and magnetic X-ray microscopy, we demonstrate the imprinting of complex chiral spin states via three-dimensional geometric effects at the nanoscale. By balancing dipolar and exchange interactions in an artificial ferromagnetic double-helix nanostructure, we create magnetic domains and domain walls with a well-defined spin chirality, determined solely by the chiral geometry. We further demonstrate the ability to create confined 3D spin textures and topological defects by locally interfacing geometries of opposite chirality. The ability to create chiral spin textures via 3D nanopatterning alone enables exquisite control over the properties and location of complex topological magnetic states, of great importance for the development of future metamaterials and devices in which chirality provides enhanced functionality. ; This work was funded by EPSRC Early Career Fellowship EP/M008517/1, the Winton Program for the Physics of Sustainability, and the EU CELINA COST action. D.S.-H. acknowledges a Girton College Pfeiffer scholarship and support from the EPSRC CDT in Nanoscience and Nanotechnology. A.H.-R. and S.M.V. acknowledge funding from the EU Horizon 2020 program through Marie Skłodowska-Curie Action H2020-MSCA-IF-2016-74695. C.D. acknowledges funding from Leverhulme Trust (ECF-2018-016), Isaac Newton Trust (18-08), and a L'Oréal-UNESCO UK and Ireland Fellowship for Women in Science 2019. Funding by the Spanish Ministry of Science is acknowledged, grants MAT2017-82970-C2-1-R, MAT2017-82970-C2-2-R and MAT2018-102627-T, and by Aragon Government (Construyendo Europa desde Aragón), grant E13_20R including European Social Fund. J.P.-N. acknowledges MINECO funding BES-2015-072950. S.M.V. appreciates support from EPSRC EP/M024423/1. P.F. was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, Contract No. DE-AC02-05-CH11231 (NEMM program MSMAG). These experiments were performed at MISTRAL beamline at ALBA Synchrotron with the collaboration of ALBA staff and CALIPSOplus (Grant 730872) funding. ; Peer reviewed

Spanish MINECO [FIS 2013-45469, FIS2016-76058]; FICYT-Asturias [FC-GRUPIN14-040]; European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie [H2020-MSCA-IF-2016-746958]

(.) Funding by the Spanish Ministry of Science is acknowledged, grants MAT2017-82970-C2-1-R, MAT2017-82970-C2-2-R and MAT2018-102627-T, and by Aragón Government (Construyendo Europa desde Aragón), grant E13_20R including European Social Fund. J.P.-N. acknowledges MINECO funding BES-2015-072950. (.)