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Scientific Reports volume 12, Article number: 10786 (2022)
Collective skyrmion motion under the influence of an additional interfacial spin-transfer torque
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Here we study the effect of an additional interfacial spin-transfer torque, as well as the well-established spin–orbit torque and bulk spin-transfer torque, on skyrmion collections—group of skyrmions dense enough that they are not isolated from one another—in ultrathin heavy metal/ferromagnetic multilayers, by comparing modelling with experimental results. Using a skyrmion collection with a range of skyrmion diameters and landscape disorder, we study the dependence of the skyrmion Hall angle on diameter and velocity, as well as the velocity as a function of diameter. We show that inclusion of the interfacial spin-transfer torque results in reduced skyrmion Hall angles, with values close to experimental results. We also show that for skyrmion collections the velocity is approximately independent of diameter, in marked contrast to the motion of isolated skyrmions, as the group of skyrmions move together at an average group velocity. Moreover, the calculated skyrmion velocities are comparable to those obtained in experiments when the interfacial spin-transfer torque is included. Our results thus show the significance of the interfacial spin-transfer torque in ultrathin magnetic multilayers, which helps to explain the low skyrmion Hall angles and velocities observed in experiment. We conclude that the interfacial spin-transfer torque should be considered in numerical modelling for reproduction of experimental results.
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our research
Computer Physics Communications, 279 (2022) 108455
HP - A code for the calculation of Hubbard parameters using density-functional perturbation theory
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We introduce HP, an implementation of density-functional perturbation theory, designed to compute Hubbard parameters (on-site U and inter-site V) in the framework of DFT+U and DFT+U+V. The code does not require the use of computationally expensive supercells of the traditional linear-response approach; instead, unit cells are used with monochromatic perturbations that significantly reduce the computational cost of determining Hubbard parameters. HP is an open-source software distributed under the terms of the GPL as a component of Quantum ESPRESSO. As with other components, HP is optimized to run on a variety of different platforms, from laptops to massively parallel architectures, using native mathematical libraries (LAPACK and FFTW) and a hierarchy of custom parallelization layers built on top of MPI. The effectiveness of the code is showcased by computing Hubbard parameters self-consistently for the phospho-olivine LixMn1/2Fe1/2PO4 (x=0,1/2,1) and by highlighting the accuracy of predictions of the geometry and Li intercalation voltages.
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from our users
Materials Science and Engineering: B Volume 283, September 2022, 115821
Morphology and composition of nanoinclusions in (Fe, Ni)(0.25)TiSe2
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A nanocomposite material consisting of (Fe,Ni)4Se5 and Ti3Se4 nanocrystals coherently bounded with the (Fe, Ni)(0.25)TiSe2 substrate was obtained during the synthesis of the (Fe, Ni)(x)TiSe2 bi-intercalation compound from the mixture of F0.25TiSe2 and Ni0.25TiSe2. The morphology of these composite crystals has been studied using optical, scanning electron and atomic force microscopy. The electronic structure of the inclusions was studied using X-ray scanning photoelectron microscopy (SPEM). We have shown that (Fe,Ni)(4)Se-5 and Ti3Se4 inclusions grow simultaneously with (Fe,Ni)xTiSe(2) substrate crystal on its (001) plane. The lateral growth of the (Fe,Ni)xTiSe(2) crystal is accompanied by the "capturing " of the (Fe,Ni)4Se5 and Ti3Se4 inclusions by the (Fe,Ni)(0.25)TiSe2 substrate resulting in the formation of the composite crystal.
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Deliverables view all
WP15 - JA5 - Correlative Nano-Spectroscopy and Nano-Diffraction
D15.2 - Image Registration Procedures
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This deliverable report 15.2 “Image registration procedures” of working package WP15 of NFFA-- Europe|PILOT (NEP) project aims to establish a unified and harmonized GUI platform for correlative experiments utilizing image registration and hierarchical markers for one-to-one and simultaneous microscopic and spectroscopic imaging. With this deliverable, DESY has developed a python-based GUI image registration software for correlative nano-spectroscopy and nano-diffraction that incorporates the nano-object transfer and positioning developed within the previous NFFA-Europe project, and additionally integrates image registration tools for further automatization.
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WP12 - JA2 - X-ray Wavefront Metrology, Correction and Manipulation
D12.1 - Fabrication of hard X-ray aberration correctors
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We report on the fabrication of hard X-ray aberration correctors to improve the performance of nanofocusing X-ray lenses by correcting the shape deviations that arise due to fluctuations and anisotropies during the manufacture of X-ray optics. After carefully characterizing the aberrations of the focusing X-ray lens, the tailored profile of a correction phase plate can be inferred. In this deliverable, we have developed the micro and nanofabrication processes for the production of the refractive phase plates by two-photon polymerization based 3D printing. The refractive phase plate is made of polymer, which introduces the required phase shift corrections while hardly introducing any extra absorption. The process parameters have been optimized to obtain the tailored aberration correction profiles. The refractive phase plates have been produced on multiple substrates such as silicon, silicon nitride and diamond membranes and they can be fabricated reliably and on-demand. The methods and procedures to easily align the focusing optics and the refractive phase plate are currently under development.
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WP9 - VA – Virtual Access
D9.1 - Deployment of the VA service prototypes
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Virtual Access (VA) is a novel service offered in NEP. It comprises innovative online simulation services, databases, machine learning services, data and metadata services, which will be seamlessly integrated into the NEP infrastructure and provided as cloud services to authenticated users. The access will be provided by the facilities hosting the services. Each Access Provider will operate its own infrastructure, made of one or more installations. All involved Access Providers will offer identified User Access to the VA services under their own schemes based on institutional policies. Part of the online data services that will be made available as VA are currently (or will be) developed in the Joint Activity (JA) 6 on FAIR data approach. According to the NEP proposal, seven services are planned, even though scouting activities to enlarge the offer are foreseen. The services are at different stages of development, and will be gradually completed and integrated into the offer. This deliverable presents the first prototype of a VA service: the MetaRepo, a metadata repository to register and validate Metadata Schemas and Metadata Documents. The document is structured as follows: Section 1 describes the MetaRepo service, and Section 2 shows the functionalities of its Graphical User Interface (GUI). Being the purpose of this Section only demonstrative, for the sake of simplicity the functionalities of the MetaRepo GUI are shown on basic examples instead of being applied to a real NEP use case. This choice has been made to prevent the confusion which might arise due to the complexity of the Metadata Schemas. A real usage example is presented in Milestone 10. Section 3 shows how the Authorization and Authentication has been implemented for the MetaRepo. Section 4 explains how the monitoring of user accesses and actions is performed.
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Transnational Access Statistics
18 calls for access
617 proposals submitted
64% rate of acceptance
31% with Large Scale Facilities
12% with theory
12% with industry
~3 average users per proposal
58 countries applying
1840 lab sessions