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| Author | Savchenko, T.M.; Buzzi, M.; Howald, L.; Ruta, S.; Vijayakumar, J.; Timm, M.; Bracher, D.; Saha, S.; Derlet, P.M.; Béché, A.; Verbeeck, J.; Chantrell, R.W.; Vaz, C.A.F.; Nolting, F.; Kleibert, A. | ||||
| Title | Single femtosecond laser pulse excitation of individual cobalt nanoparticles | Type | A1 Journal article | ||
| Year | 2020 | Publication | Physical Review B | Abbreviated Journal | Phys Rev B |
| Volume | 102 | Issue | 20 | Pages | 205418 |
| Keywords | A1 Journal article; Electron microscopy for materials research (EMAT) | ||||
| Abstract | Laser-induced manipulation of magnetism at the nanoscale is a rapidly growing research topic with potential for applications in spintronics. In this work, we address the role of the scattering cross section, thermal effects, and laser fluence on the magnetic, structural, and chemical stability of individual magnetic nanoparticles excited by single femtosecond laser pulses. We find that the energy transfer from the fs laser pulse to the nanoparticles is limited by the Rayleigh scattering cross section, which in combination with the light absorption of the supporting substrate and protective layers determines the increase in the nanoparticle temperature. We investigate individual Co nanoparticles (8 to 20 nm in size) as a prototypical model system, using x-ray photoemission electron microscopy and scanning electron microscopy upon excitation with single femtosecond laser pulses of varying intensity and polarization. In agreement with calculations, we find no deterministic or stochastic reversal of the magnetization in the nanoparticles up to intensities where ultrafast demagnetization or all-optical switching is typically reported in thin films. Instead, at higher fluences, the laser pulse excitation leads to photo-chemical reactions of the nanoparticles with the protective layer, which results in an irreversible change in the magnetic properties. Based on our findings, we discuss the conditions required for achieving laser-induced switching in isolated nanomagnets. | ||||
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| Language | Wos | 000589602000005 | Publication Date | 2020-11-16 | |
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| ISSN | 2469-9950 | ISBN | Additional Links | UA library record; WoS full record | |
| Impact Factor | 3.7 | Times cited | 1 | Open Access | OpenAccess |
Notes  |
This work received funding by the Swiss National Foundation (SNF) (Grants No. 200021160186 and No. 2002153540), the Swiss Nanoscience Institute (SNI) (Grant No. SNI P1502), the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 737093 (FEMTOTERABYTE), and the COST Action CA17123 (MAGNETOFON). Part of this work was performed at the SIM beamline of the Swiss Light Source (SLS), Paul Scherrer Institut, Villigen, Switzerland. Part of the simulations were undertaken on the VIKING cluster, which is a high-performance compute facility provided by the University of York. We kindly acknowledge Anja Weber from PSI for preparation of substrates with marker structures. A.B. and Jo Verbeeck acknowledge funding through FWO Project No. G093417N (“Compressed sensing enabling low dose imaging in transmission electron microscopy”) from the Flanders Research Fund. Jo Verbeeck acknowledges funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 823717 – ESTEEM3. S.S. acknowledges ETH Zurich Post-Doctoral fellowship and Marie Curie actions for people COFUND program.; esteem3JRA; esteem3reported | Approved | Most recent IF: 3.7; 2020 IF: 3.836 | ||
| Call Number | EMAT @ emat @c:irua:174273 | Serial | 6669 | ||
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| Author | Claes, J.; Partoens, B.; Lamoen, D. | ||||
| Title | Decoupled DFT-1/2 method for defect excitation energies | Type | A1 Journal Article | ||
| Year | 2023 | Publication | Physical Review B | Abbreviated Journal | Phys. Rev. B |
| Volume | 108 | Issue | 12 | Pages | 125306 |
| Keywords | A1 Journal Article; Condensed Matter Theory (CMT) ; | ||||
| Abstract | The DFT-1/2 method is a band-gap correction with GW precision at a density functional theory (DFT) computational cost. The method was also extended to correct the gap between defect levels, allowing for the calculation of optical transitions. However, this method fails when the atomic character of the occupied and unoccupied defect levels is similar as we illustrate by two examples, the tetrahedral hydrogen interstitial and the negatively charged vacancy in diamond. We solve this problem by decoupling the effect of the occupied and unoccupied defect levels and call this the decoupled DFT-1/2 method for defects. | ||||
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| Language | Wos | 001089302800003 | Publication Date | 2023-09-25 | |
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| ISSN | 2469-9950 | ISBN | Additional Links | UA library record; WoS full record | |
| Impact Factor | 3.7 | Times cited | Open Access | Not_Open_Access | |
| Notes |
This work was supported by the FWO (Research Foundation-Flanders), Project No. G0D1721N. This work was performed in part using HPC resources from the VSC (Flemish Supercomputer Center) and the HPC infrastructure of the University of Antwerp (CalcUA), both funded by the FWO-Vlaanderen and the Flemish Government department EWI (Economie, Wetenschap & Innovatie). | Approved | Most recent IF: 3.7; 2023 IF: 3.836 | ||
| Call Number | CMT @ cmt @c:irua:201287 | Serial | 8976 | ||
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| Author | Stosic, D.; Mulkers, J.; Van Waeyenberge, B.; Ludermir, T.B.; Milošević, M.V. | ||||
| Title | Paths to collapse for isolated skyrmions in few-monolayer ferromagnetic films | Type | A1 Journal article | ||
| Year | 2017 | Publication | Physical review B | Abbreviated Journal | Phys Rev B |
| Volume | 95 | Issue | 21 | Pages | 214418 |
| Keywords | A1 Journal article; Condensed Matter Theory (CMT) | ||||
| Abstract | Magnetic skyrmions are topological spin configurations in materials with chiral Dzyaloshinskii-Moriya interaction (DMI), that are potentially useful for storing or processing information. To date, DMI has been found in few bulk materials, but can also be induced in atomically thin magnetic films in contact with surfaces with large spin-orbit interactions. Recent experiments have reported that isolated magnetic skyrmions can be stabilized even near room temperature in few-atom-thick magnetic layers sandwiched between materials that provide asymmetric spin-orbit coupling. Here we present the minimum-energy path analysis of three distinct mechanisms for the skyrmion collapse, based on ab initio input and the performed atomic-spin simulations. We focus on the stability of a skyrmion in three atomic layers of Co, either epitaxial on the Pt(111) surface or within a hybrid multilayer where DMI nontrivially varies per monolayer due to competition between different symmetry breaking from two sides of the Co film. In laterally finite systems, their constrained geometry causes poor thermal stability of the skyrmion toward collapse at the boundary, which we show to be resolved by designing the high-DMI structure within an extended film with lower or no DMI. | ||||
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| Language | Wos | 000404015500001 | Publication Date | 2017-06-23 | |
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| ISSN | 2469-9950 | ISBN | Additional Links | UA library record; WoS full record; WoS citing articles | |
| Impact Factor | 3.836 | Times cited | 48 | Open Access | |
| Notes |
This work was supported by the Research Foundation, Flanders (FWO-Vlaanderen) and Brazilian agency CNPq (Grants No. 442668/2014-7 and No. 140840/2016-8). | Approved | Most recent IF: 3.836 | ||
| Call Number | CMT @ cmt @c:irua:144865 | Serial | 4704 | ||
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| Author | Mulkers, J.; Van Waeyenberge, B.; Milošević, M.V. | ||||
| Title | Tunable Snell's law for spin waves in heterochiral magnetic films | Type | A1 Journal article | ||
| Year | 2018 | Publication | Physical review B | Abbreviated Journal | Phys Rev B |
| Volume | 97 | Issue | 10 | Pages | 104422 |
| Keywords | A1 Journal article; Condensed Matter Theory (CMT) | ||||
| Abstract | Thin ferromagnetic films with an interfacially induced DMI exhibit nontrivial asymmetric dispersion relations that lead to unique and useful magnonic properties. Here we derive an analytical expression for the magnon propagation angle within the micromagnetic framework and show how the dispersion relation can be approximated with a comprehensible geometrical interpretation in the k space of the propagation of spin waves. We further explore the refraction of spin waves at DMI interfaces in heterochiral magnetic films, after deriving a generalized Snell's law tunable by an in-plane magnetic field, that yields analytical expressions for critical incident angles. The found asymmetric Brewster angles at interfaces of regions with different DMI strengths, adjustable by magnetic field, support the conclusion that heterochiral ferromagnetic structures are an ideal platform for versatile spin-wave guides. | ||||
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| Language | Wos | 000428238600006 | Publication Date | 2018-03-26 | |
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| ISSN | 2469-9950 | ISBN | Additional Links | UA library record; WoS full record; WoS citing articles | |
| Impact Factor | 3.836 | Times cited | 20 | Open Access | |
| Notes |
This work was supported by the Research Foundation- Flanders (FWO-Vlaanderen) through Project No. G098917N. | Approved | Most recent IF: 3.836 | ||
| Call Number | CMT @ cmt @c:irua:150118UA @ admin @ c:irua:150118 | Serial | 4915 | ||
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| Author | Tsirlin, A.A.; Rousochatzakis, I.; Filimonov, D.; Batuk, D.; Frontzek, M.; Abakumov, A.M. | ||||
| Title | Spin-reorientation transitions in the Cairo pentagonal magnet Bi4Fe5O13F | Type | A1 Journal article | ||
| Year | 2017 | Publication | Physical review B | Abbreviated Journal | Phys Rev B |
| Volume | 96 | Issue | 9 | Pages | 094420 |
| Keywords | A1 Journal article; Electron microscopy for materials research (EMAT) | ||||
| Abstract | We show that interlayer spins play a dual role in the Cairo pentagonal magnet Bi4Fe5O13F, on one hand mediating the three-dimensional magnetic order, and on the other driving spin-reorientation transitions both within and between the planes. The corresponding sequence of magnetic orders unraveled by neutron diffraction and Mossbauer spectroscopy features two orthogonal magnetic structures described by opposite local vector chiralities, and an intermediate, partly disordered phase with nearly collinear spins. A similar collinear phase has been predicted theoretically to be stabilized by quantum fluctuations, but Bi4Fe5O13F is very far from the relevant parameter regime. While the observed in-plane reorientation cannot be explained by any standard frustration mechanism, our ab initio band-structure calculations reveal strong single-ion anisotropy of the interlayer Fe3+ spins that turns out to be instrumental in controlling the local vector chirality and the associated interlayer order. | ||||
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| Language | Wos | 000411161700002 | Publication Date | 2017-09-19 | |
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| ISSN | 2469-9950 | ISBN | Additional Links | UA library record; WoS full record; WoS citing articles | |
| Impact Factor | 3.836 | Times cited | 7 | Open Access | OpenAccess |
| Notes |
We are grateful to J.-M. Perez-Mato and Dmitry Khalyavin for valuable discussions on the magnetic structures and symmetries. D.F. and A.A. are grateful to the Russian Science Foundation (Grant No. 14-13-00680) for support. A.T. was supported by the Federal Ministry for Education and Research through the Sofja Kovalevskaya Award of the Alexander von Humboldt Foundation. This work is based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institut, Villigen, Switzerland. | Approved | Most recent IF: 3.836 | ||
| Call Number | EMAT @ emat @c:irua:146748 | Serial | 4774 | ||
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| Author | Kleibert, A.; Balan, A.; Yanes, R.; Derlet, P.M.; Vaz, C.A.F.; Timm, M.; Fraile Rodríguez, A.; Béché, A.; Verbeeck, J.; Dhaka, R.S.; Radovic, M.; Nowak, U.; Nolting, F. | ||||
| Title | Direct observation of enhanced magnetism in individual size- and shape-selected 3d transition metal nanoparticles | Type | A1 Journal article | ||
| Year | 2017 | Publication | Physical review B | Abbreviated Journal | Phys Rev B |
| Volume | 95 | Issue | 95 | Pages | 195404 |
| Keywords | A1 Journal article; Electron microscopy for materials research (EMAT) | ||||
| Abstract | Magnetic nanoparticles are critical building blocks for future technologies ranging from nanomedicine to spintronics. Many related applications require nanoparticles with tailored magnetic properties. However, despite significant efforts undertaken towards this goal, a broad and poorly understood dispersion of magnetic properties is reported, even within monodisperse samples of the canonical ferromagnetic 3d transition metals. We address this issue by investigating the magnetism of a large number of size- and shape-selected, individual nanoparticles of Fe, Co, and Ni using a unique set of complementary characterization techniques. At room temperature, only superparamagnetic behavior is observed in our experiments for all Ni nanoparticles within the investigated sizes, which range from 8 to 20 nm. However, Fe and Co nanoparticles can exist in two distinct magnetic states at any size in this range: (i) a superparamagnetic state, as expected from the bulk and surface anisotropies known for the respective materials and as observed for Ni, and (ii) a state with unexpected stable magnetization at room temperature. This striking state is assigned to significant modifications of the magnetic properties arising from metastable lattice defects in the core of the nanoparticles, as concluded by calculations and atomic structural characterization. Also related with the structural defects, we find that the magnetic state of Fe and Co nanoparticles can be tuned by thermal treatment enabling one to tailor their magnetic properties for applications. This paper demonstrates the importance of complementary single particle investigations for a better understanding of nanoparticle magnetism and for full exploration of their potential for applications. | ||||
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| Language | Wos | 000400665300002 | Publication Date | 2017-05-05 | |
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| ISSN | 2469-9950 | ISBN | Additional Links | UA library record; WoS full record; WoS citing articles | |
| Impact Factor | 3.836 | Times cited | 21 | Open Access | OpenAccess |
| Notes |
We thank A. Weber, R. Schelldorfer, and J. Krbanjevic (Paul Scherrer Institut) for technical assistance. This paper was supported by the Swiss Nanoscience Institute, University of Basel. A.F.R. acknowledges support from the MICIIN “Ramón y Cajal” Programme. A.B. and J.V. acknowledge funding from the European Union under the European Research Council (ERC) Starting Grant No. 278510 VORTEX and under a contract for Integrated Infrastructure Initiative ESTEEM2 No. 312483. R.Y. and U.N. thank the Deutsche Forschungsgemeinschaft for financial support via Sonderforschungsbereich 1214. Part of this work was performed at the Surface/Interface: Microscopy (SIM) beamline of the Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. | Approved | Most recent IF: 3.836 | ||
| Call Number | EMAT @ emat @ c:irua:143634UA @ admin @ c:irua:143634 | Serial | 4575 | ||
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| Author | Bercx, M.; Partoens, B.; Lamoen, D. | ||||
| Title | Quantitative modeling of secondary electron emission from slow-ion bombardment on semiconductors | Type | A1 Journal article | ||
| Year | 2019 | Publication | Physical review B | Abbreviated Journal | Phys Rev B |
| Volume | 99 | Issue | 8 | Pages | 085413 |
| Keywords | A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT) | ||||
| Abstract | When slow ions incident on a surface are neutralized, the excess potential energy is passed on to an electron inside the surface, leading to emission of secondary electrons. The microscopic description of this process, as well as the calculation of the secondary electron yield, is a challenging problem due to its complexity as well as its sensitivity to surface properties. One of the first quantitative descriptions was articulated in the 1950s by Hagstrum, who based his calculation on a parametrization of the density of states of the material. In this paper, we present a model for calculating the secondary electron yield, derived from Hagstrum’s initial approach. We use first-principles density functional theory calculations to acquire the necessary input and introduce the concept of electron cascades to Hagstrum’s model in order to improve the calculated spectra, as well as remove its reliance on fitting parameters. We apply our model to He+ and Ne+ ions incident on Ge(111) and Si(111) and obtain yield spectra that match closely to the experimental results of Hagstrum. |
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| Language | Wos | 000458367800010 | Publication Date | 2019-02-11 | |
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| ISSN | 2469-9950 | ISBN | Additional Links | UA library record; WoS full record; WoS citing articles | |
| Impact Factor | 3.836 | Times cited | 5 | Open Access | OpenAccess |
| Notes |
We would like to thank Prof. D. Depla for the useful discussions on the secondary electron yield. Furthermore, we acknowledge financial support of FWO-Vlaanderen through project G.0216.14N. The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center) and the HPC infrastructure of the University of Antwerp (CalcUA), both funded by the FWOVlaanderen and the Flemish Government-department EWI. | Approved | Most recent IF: 3.836 | ||
| Call Number | EMAT @ emat @UA @ admin @ c:irua:157174 | Serial | 5154 | ||
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