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Adhikari S, Li J, Wang Y, Ruijs L, Liu J, Koopmans B, Orrit M, Lavrijsen R. Optical Monitoring of the Magnetization Switching of Single Synthetic-Antiferromagnetic Nanoplatelets with Perpendicular Magnetic Anisotropy. ACS Photonics 2023; 10:1512-1518. [PMID: 37215319 PMCID: PMC10197163 DOI: 10.1021/acsphotonics.3c00123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Indexed: 05/24/2023]
Abstract
Synthetic antiferromagnetic nanoplatelets (NPs) with a large perpendicular magnetic anisotropy (SAF-PMA NPs) have a large potential in future local mechanical torque-transfer applications for e.g., biomedicine. However, the mechanisms of magnetization switching of these structures at the nanoscale are not well understood. Here, we have used a simple and relatively fast single-particle optical technique that goes beyond the diffraction limit to measure photothermal magnetic circular dichroism (PT MCD). This allows us to study the magnetization switching as a function of applied magnetic field of single 122 nm diameter SAF-PMA NPs with a thickness of 15 nm. We extract and discuss the differences between the switching field distributions of large ensembles of NPs and of single NPs. In particular, single-particle PT MCD allows us to address the spatial and temporal heterogeneity of the magnetic switching fields of the NPs at the single-particle level. We expect this new insight to help understand better the dynamic torque transfer, e.g., in biomedical and microfluidic applications.
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Affiliation(s)
- S. Adhikari
- Huygens-Kamerlingh
Onnes Laboratory, LION, 2300 RA Leiden, Netherlands
| | - J. Li
- Department
of Applied Physics, Eindhoven University
of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
| | - Y. Wang
- Huygens-Kamerlingh
Onnes Laboratory, LION, 2300 RA Leiden, Netherlands
- School
of Mechatronics Engineering, Harbin Institute
of Technology, Harbin 150001, P. R. China
| | - L. Ruijs
- Department
of Applied Physics, Eindhoven University
of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
| | - J. Liu
- School
of Mechatronics Engineering, Harbin Institute
of Technology, Harbin 150001, P. R. China
| | - B. Koopmans
- Department
of Applied Physics, Eindhoven University
of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
| | - M. Orrit
- Huygens-Kamerlingh
Onnes Laboratory, LION, 2300 RA Leiden, Netherlands
| | - R. Lavrijsen
- Department
of Applied Physics, Eindhoven University
of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
- Institute
for Complex Molecular Systems, Eindhoven
University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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2
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Beens M, de Mare KA, Duine RA, Koopmans B. Spin-polarized hot electron transport versus spin pumping mediated by local heating. J Phys Condens Matter 2022; 35:035803. [PMID: 36368045 DOI: 10.1088/1361-648x/aca24e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Accepted: 11/11/2022] [Indexed: 06/16/2023]
Abstract
A 'toy model'-aimed at capturing the essential physics-is presented that jointly describes spin-polarized hot electron transport and spin pumping driven by local heating. These two processes both contribute to spin-current generation in laser-excited magnetic heterostructures. The model is used to compare the two contributions directly. The spin-polarized hot electron current is modeled as one generation of hot electrons with a spin-dependent excitation and relaxation scheme. Upon decay, the excess energy of the hot electrons is transferred to a thermalized electron bath. The elevated electron temperature leads to an increased rate of electron-magnon scattering processes and yields a local accumulation of spin. This process is dubbed as spin pumping by local heating. The built-up spin accumulation is effectively driven out of the ferromagnetic system by (interfacial) electron transport. Within our model, the injected spin current is dominated by the contribution resulting from spin pumping, while the hot electron spin current remains relatively small. We derive that this observation is related to the ratio between the Fermi temperature and Curie temperature, and we show what other fundamental parameters play a role.
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Affiliation(s)
- M Beens
- Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
| | - K A de Mare
- Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
| | - R A Duine
- Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
- Institute for Theoretical Physics, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht, The Netherlands
| | - B Koopmans
- Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
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3
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Guimarães MHD, Koopmans B. Spin Accumulation and Dynamics in Inversion-Symmetric van der Waals Crystals. Phys Rev Lett 2018; 120:266801. [PMID: 30004759 DOI: 10.1103/physrevlett.120.266801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 04/25/2018] [Indexed: 06/08/2023]
Abstract
Inversion-symmetric materials are forbidden to show an overall spin texture in their band structure in the presence of time-reversal symmetry. However, in van der Waals materials which lack inversion symmetry within a single layer, it has been proposed that a layer-dependent spin texture can arise leading to a coupled spin-layer degree of freedom. Here we use time-resolved Kerr rotation in inversion-symmetric WSe_{2} and MoSe_{2} bulk crystals to study this spin-layer polarization and unveil its dynamics. Our measurements show that the spin-layer relaxation time in WSe_{2} is limited by phonon scattering at high temperatures and that the interlayer hopping can be tuned by a small in-plane magnetic field at low temperatures, enhancing the relaxation rates. We find a significantly lower lifetime for MoSe_{2} which agrees with theoretical expectations of a spin-layer polarization stabilized by the larger spin-orbit coupling in WSe_{2}.
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Affiliation(s)
- M H D Guimarães
- Department of Applied Physics, Eindhoven University of Technology, Eindhoven, Netherlands
| | - B Koopmans
- Department of Applied Physics, Eindhoven University of Technology, Eindhoven, Netherlands
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4
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Marchisella E, Wijnands R, Koopmans B, Spijker S, Loos M. Constitutive loss and acute pharmacological manipulation of ErbB4 signaling do not affect attention and inhibitory control in mice. Genes Brain Behav 2017; 17:56-69. [PMID: 28792672 DOI: 10.1111/gbb.12402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Revised: 06/30/2017] [Accepted: 07/19/2017] [Indexed: 02/03/2023]
Abstract
The receptor tyrosine kinase ErbB4 and its ligand trophic factors of the neuregulin (NRG) family have been associated with schizophrenia and other mental disorders in human genetic studies. In vivo studies in mice have shown how abnormal Nrg-ErbB4 signaling leads to deviant behaviors relevant to distinct aspects of schizophrenia, including hyperactivity, sensory gating deficits, working and spatial memory deficits and impaired social behavior. However, so far little is known on the role of ErbB4 in attention and inhibitory control, two aspects of executive functions that are impaired in schizophrenia. Here we investigated the effects of constitutive loss of ErbB4 in the central nervous system of mice on performance in a 5-choice serial reaction time task (5CSRTT) assessing attention and inhibitory control. In this task, ErbB4-/- mice did not show deficits in various parameters of attention, and premature responses as measure of inhibitory control. Nonetheless, ErbB4-/- mice recapitulated a specific set of behavioral phenotypes associated with schizophrenia, including a deficit in spatial learning and memory in the Barnes Maze and in contextual fear learning, and a trend for a deficit in sensorimotor gating. Furthermore, we investigated the effect of acute pharmacological inhibition of ErbB tyrosine kinase receptor using the pan-ErbB kinase inhibitor JNJ-28871063 (JNJ), in an automated version of the 5CSRTT. JNJ did not affect attention and inhibitory control. In conclusion, our data suggest no direct involvement of a classical Nrg-ErbB4 pathway in attention and inhibitory control in mice, while it confirms the involvement of this pathway in other domains relevant to schizophrenia.
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Affiliation(s)
| | | | | | - S Spijker
- Department of Molecular & Cellular Neurobiology, Center for Neurogenomics and Cognitive research, Neuroscience Campus Amsterdam, VU University, De Boelelaan, The Netherlands
| | - M Loos
- Sylics (Synaptologics B.V.), Amsterdam.,Department of Molecular & Cellular Neurobiology, Center for Neurogenomics and Cognitive research, Neuroscience Campus Amsterdam, VU University, De Boelelaan, The Netherlands
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5
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Stoll T, Zafeiropoulos G, Dogan I, Genuit H, Lavrijsen R, Koopmans B, Tsampas M. Visible-light-promoted gas-phase water splitting using porous WO 3 /BiVO 4 photoanodes. Electrochem commun 2017. [DOI: 10.1016/j.elecom.2017.07.019] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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6
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Bergeard N, Hehn M, Mangin S, Lengaigne G, Montaigne F, Lalieu MLM, Koopmans B, Malinowski G. Hot-Electron-Induced Ultrafast Demagnetization in Co/Pt Multilayers. Phys Rev Lett 2016; 117:147203. [PMID: 27740830 DOI: 10.1103/physrevlett.117.147203] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Indexed: 05/23/2023]
Abstract
Using specially engineered structures to tailor the optical absorption in a metallic multilayer, we analyze the magnetization dynamics of a Co/Pt multilayer buried below a thick Cu layer. We demonstrate that hot electrons alone can very efficiently induce ultrafast demagnetization. Simulations based on hot electron ballistic transport implemented within a microscopic model that accounts for local dissipation of angular momentum nicely reproduce the experimental results, ruling out contribution of pure thermal transport.
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Affiliation(s)
- N Bergeard
- Institut Jean Lamour, CNRS UMR 7198, Universitè de Lorraine, 54506 Vandoeuvre-lès-Nancy, France
| | - M Hehn
- Institut Jean Lamour, CNRS UMR 7198, Universitè de Lorraine, 54506 Vandoeuvre-lès-Nancy, France
| | - S Mangin
- Institut Jean Lamour, CNRS UMR 7198, Universitè de Lorraine, 54506 Vandoeuvre-lès-Nancy, France
| | - G Lengaigne
- Institut Jean Lamour, CNRS UMR 7198, Universitè de Lorraine, 54506 Vandoeuvre-lès-Nancy, France
| | - F Montaigne
- Institut Jean Lamour, CNRS UMR 7198, Universitè de Lorraine, 54506 Vandoeuvre-lès-Nancy, France
| | - M L M Lalieu
- Department of Applied Physics, center for NanoMaterials (cNM) Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - B Koopmans
- Department of Applied Physics, center for NanoMaterials (cNM) Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - G Malinowski
- Institut Jean Lamour, CNRS UMR 7198, Universitè de Lorraine, 54506 Vandoeuvre-lès-Nancy, France
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7
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Sharma N, van Mourik RA, Yin Y, Koopmans B, Parkin SSP. Focused-electron-beam-induced-deposited cobalt nanopillars for nanomagnetic logic. Nanotechnology 2016; 27:165301. [PMID: 26941232 DOI: 10.1088/0957-4484/27/16/165301] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Nanomagnetic logic (NML) intends to alleviate problems of continued miniaturization of CMOS-based electronics, such as energy dissipation through heat, through advantages such as low power operation and non-volatile magnetic elements. In line with recent breakthroughs in NML with perpendicularly magnetized elements formed from thin films, we have fabricated NML inverter chains from Co nanopillars by focused electron beam induced deposition (FEBID) that exhibit shape-induced perpendicular magnetization. The flexibility of FEBID allows optimization of NML structures. Simulations reveal that the choice of nanopillar dimensions is critical to obtain the correct antiferromagnetically coupled configuration. Experiments carrying the array through a clocking cycle using the Oersted field from an integrated Cu wire show that the array responds to the clocking cycle.
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Affiliation(s)
- N Sharma
- Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands
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8
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van den Brink A, Vermijs G, Solignac A, Koo J, Kohlhepp JT, Swagten HJM, Koopmans B. Field-free magnetization reversal by spin-Hall effect and exchange bias. Nat Commun 2016; 7:10854. [PMID: 26940861 PMCID: PMC5411711 DOI: 10.1038/ncomms10854] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Accepted: 01/27/2016] [Indexed: 11/09/2022] Open
Abstract
As the first magnetic random access memories are finding their way onto the market, an important issue remains to be solved: the current density required to write magnetic bits becomes prohibitively high as bit dimensions are reduced. Recently, spin–orbit torques and the spin-Hall effect in particular have attracted significant interest, as they enable magnetization reversal without high current densities running through the tunnel barrier. For perpendicularly magnetized layers, however, the technological implementation of the spin-Hall effect is hampered by the necessity of an in-plane magnetic field for deterministic switching. Here we interface a thin ferromagnetic layer with an anti-ferromagnetic material. An in-plane exchange bias is created and shown to enable field-free S HE-driven magnetization reversal of a perpendicularly magnetized Pt/Co/IrMn structure. Aside from the potential technological implications, our experiment provides additional insight into the local spin structure at the ferromagnetic/anti-ferromagnetic interface. Future information storage technology may exploit electrical currents to write the states of ferromagnetic nanoelements via spin torque effects. Here, the authors demonstrate such behaviour promoted by exchange bias from an interfaced antiferromagnet, which may help overcome practical device limitations.
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Affiliation(s)
- A van den Brink
- Eindhoven University of Technology, PO Box 513, Noord-Brabant, 5600 MB Eindhoven, The Netherlands
| | - G Vermijs
- Eindhoven University of Technology, PO Box 513, Noord-Brabant, 5600 MB Eindhoven, The Netherlands
| | - A Solignac
- Eindhoven University of Technology, PO Box 513, Noord-Brabant, 5600 MB Eindhoven, The Netherlands.,SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay 91191 Gif-sur-Yvette, France
| | - J Koo
- Eindhoven University of Technology, PO Box 513, Noord-Brabant, 5600 MB Eindhoven, The Netherlands
| | - J T Kohlhepp
- Eindhoven University of Technology, PO Box 513, Noord-Brabant, 5600 MB Eindhoven, The Netherlands
| | - H J M Swagten
- Eindhoven University of Technology, PO Box 513, Noord-Brabant, 5600 MB Eindhoven, The Netherlands
| | - B Koopmans
- Eindhoven University of Technology, PO Box 513, Noord-Brabant, 5600 MB Eindhoven, The Netherlands
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9
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Córdoba R, Barcones B, Roelfsema E, Verheijen MA, Mulders JJL, Trompenaars PHF, Koopmans B. Functional nickel-based deposits synthesized by focused beam induced processing. Nanotechnology 2016; 27:065303. [PMID: 26759183 DOI: 10.1088/0957-4484/27/6/065303] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Functional nanostructures fabricated by focused electron/ion beam induced processing (FEBIP/FIBIP) open a promising route for applications in nanoelectronics. Such developments rely on the exploration of new advanced materials. We report here the successful fabrication of nickel-based deposits by FEBIP/FIBIP using bis(methyl cyclopentadienyl)nickel as a precursor. In particular, binary compounds such as nickel oxide (NiO) are synthesized by using an in situ two-step process at room temperature. By this method, as-grown Ni deposits transform into homogeneous NiO deposits using focused electron beam irradiation under O2 flux. This procedure is effective in producing highly pure NiO deposits with resistivity of 2000 Ωcm and a polycrystalline structure with face-centred cubic lattice and grains of 5 nm. We demonstrate that systems based on NiO deposits displaying resistance switching and an exchange-bias effect could be grown by FEBIP using optimized parameters. Our results provide a breakthrough towards using these techniques for the fabrication of functional nanodevices.
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Affiliation(s)
- R Córdoba
- Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
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10
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Abstract
We introduce an alternative type of probe for scanning tunneling microscopy (STM). Instead of using a needle-like tip made from a piece of metallic wire, a sharp-edged cleaved insulating substrate, which is initially covered by a thin conductive film, is used. The sharp tip is formed at the intersection of the two cleaved sides. Using this approach a variety of materials for STM probes can be used, and functionalization of STM probes is possible. The working principle of different probes made of metallic (Pt, Co, and CoB), indium-tin oxide, as well as Cu/Pt and Co/Pt multilayer films are demonstrated by STM imaging of clean Cu(001) and Cu(111) surfaces as well as the epitaxial Co clusters on Cu(111).
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Affiliation(s)
- T Siahaan
- Department of Applied Physics, Eindhoven University of Technology, 5600 MB, The Netherlands
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11
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Giniatullina A, Maroteaux G, Geerts CJ, Koopmans B, Loos M, Klaassen R, Chen N, van der Schors RC, van Nierop P, Li KW, de Jong J, Altrock WD, Cornelisse LN, Toonen RF, van der Sluis S, Sullivan PF, Stiedl O, Posthuma D, Smit AB, Groffen AJ, Verhage M. Functional characterization of the PCLO p.Ser4814Ala variant associated with major depressive disorder reveals cellular but not behavioral differences. Neuroscience 2015; 300:518-38. [PMID: 26045179 DOI: 10.1016/j.neuroscience.2015.05.047] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 05/17/2015] [Accepted: 05/20/2015] [Indexed: 12/14/2022]
Abstract
Genome-wide association studies have suggested a role for a genetic variation in the presynaptic gene PCLO in major depressive disorder (MDD). As with many complex traits, the PCLO variant has a small contribution to the overall heritability and the association does not always replicate. One variant (rs2522833, p.Ser4814Ala) is of particular interest given that it is a common, nonsynonymous exon variant near a calcium-sensing part of PCLO. It has been suggested that the molecular effects of such variations penetrate to a variable extent in the population due to phenotypic and genotypic heterogeneity at the population level. More robust effects may be exposed by studying such variations in isolation, in a more homogeneous context. We tested this idea by modeling PCLO variation in a mouse knock-in model expressing the Pclo(SA)(/)(SA) variant. In the highly homogeneous background of inbred mice, two functional effects of the SA-variation were observed at the cellular level: increased synaptic Piccolo levels, and 30% increased excitatory synaptic transmission in cultured neurons. Other aspects of Piccolo function were unaltered: calcium-dependent phospholipid binding, synapse formation in vitro, and synaptic accumulation of synaptic vesicles. Moreover, anxiety, cognition and depressive-like behavior were normal in Pclo(SA)(/)(SA) mice. We conclude that the PCLO p.Ser4814Ala missense variant produces mild cellular phenotypes, which do not translate into behavioral phenotypes. We propose a model explaining how (subtle) cellular phenotypes do not penetrate to the mouse behavioral level but, due to genetic and phenotypic heterogeneity and non-linearity, can produce association signals in human population studies.
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Affiliation(s)
- A Giniatullina
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - G Maroteaux
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - C J Geerts
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - B Koopmans
- Sylics (Synaptologics BV), Amsterdam, The Netherlands
| | - M Loos
- Sylics (Synaptologics BV), Amsterdam, The Netherlands
| | - R Klaassen
- Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - N Chen
- Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - R C van der Schors
- Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - P van Nierop
- Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - K W Li
- Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - J de Jong
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - W D Altrock
- Department of Neurochemistry and Molecular Biology, Leibniz Institute for Neurobiology, Magdeburg, Germany
| | - L N Cornelisse
- Department of Clinical Genetics, Section Complex Trait Genetics, VU University Medical Center, Amsterdam, The Netherlands
| | - R F Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - S van der Sluis
- Department of Clinical Genetics, Section Complex Trait Genetics, VU University Medical Center, Amsterdam, The Netherlands
| | - P F Sullivan
- Department of Genetics, University of North Carolina, Chapel Hill, NC, USA; Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
| | - O Stiedl
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands; Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - D Posthuma
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands; Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
| | - A B Smit
- Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands
| | - A J Groffen
- Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
| | - M Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands; Department of Clinical Genetics, Section Complex Trait Genetics, VU University Medical Center, Amsterdam, The Netherlands.
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12
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Sharma N, Vugts P, Daniels C, Keuning W, Kohlhepp JT, Kurnosikov O, Koopmans B. Multi-channel Andreev reflection in Co-W nanocontacts fabricated using focused electron/ion beam induced deposition. Nanotechnology 2014; 25:495201. [PMID: 25409909 DOI: 10.1088/0957-4484/25/49/495201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report multi-channel electron transport in nano-contacts fabricated using focused electron beam induced deposited (FEBID) cobalt and focused ion beam induced deposited (FIBID) tungsten. Anomalous Andreev reflection (AR) effect is observed to which the conventional Blonder-Tinkham-Klapwijk (BTK) fit cannot be applied. In specific, we have observed multiple number of shoulders near the AR peak, whose origin is unknown in literature. We explain this effect based on a simple model that takes into account the material properties of the FIBID grown W superconductor, as well as the specific interface properties that are an outcome of using FEBID/FIBID as a fabrication technique. We show that numerical calculations using the BTK approximation based on the consideration of multiple channels generate similar shoulders as we observed in the AR experiments. Electrical measurements and x-ray photoemission spectroscopy carried out on FIBID W deposits puts additional evidence towards multi-channel current transport occuring at the interface of the nanocontacts.
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Affiliation(s)
- N Sharma
- Department of Applied Physics, Center for NanoMaterials and COBRA Research Institute, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
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13
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Schellekens AJ, Kuiper KC, de Wit RRJC, Koopmans B. Ultrafast spin-transfer torque driven by femtosecond pulsed-laser excitation. Nat Commun 2014; 5:4333. [PMID: 25007881 DOI: 10.1038/ncomms5333] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 06/06/2014] [Indexed: 11/09/2022] Open
Abstract
Spin currents have an important role in many proposed spintronic devices, as they govern the switching process of magnetic bits in random access memories or drive domain wall motion in magnetic shift registers. The generation of these spin currents has to be fast and energy efficient for realization of these envisioned devices. Recently it has been shown that femtosecond pulsed-laser excitation of thin magnetic films creates intense and ultrafast spin currents. Here we utilize this method to change the orientation of the magnetization in a magnetic bilayer by spin-transfer torque on sub-picosecond timescales. By analysing the dynamics of the magnetic bilayer after laser excitation, the rich physics governing ultrafast spin-transfer torque are elucidated opening up new pathways to ultrafast magnetization reversal, but also providing a new method to quantify optically induced spin currents generated on femtosecond timescales.
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Affiliation(s)
- A J Schellekens
- Department of Applied Physics, Center for NanoMaterials (cNM), Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
| | - K C Kuiper
- Department of Applied Physics, Center for NanoMaterials (cNM), Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
| | - R R J C de Wit
- Department of Applied Physics, Center for NanoMaterials (cNM), Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
| | - B Koopmans
- Department of Applied Physics, Center for NanoMaterials (cNM), Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
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14
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Janssen P, Cox M, Wouters S, Kemerink M, Wienk M, Koopmans B. Tuning organic magnetoresistance in polymer-fullerene blends by controlling spin reaction pathways. Nat Commun 2013; 4:2286. [DOI: 10.1038/ncomms3286] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2013] [Accepted: 07/10/2013] [Indexed: 11/09/2022] Open
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15
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Schellekens AJ, Koopmans B. Comparing ultrafast demagnetization rates between competing models for finite temperature magnetism. Phys Rev Lett 2013; 110:217204. [PMID: 23745920 DOI: 10.1103/physrevlett.110.217204] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Indexed: 06/02/2023]
Abstract
We investigate a recent controversy in ultrafast magnetization dynamics by comparing the demagnetization rates from two frequently used but competing descriptions for finite temperature magnetism, namely a rigid band structure Stoner-like approach and a system of localized spins. The calculations on the localized spin system show a demagnetization rate and time comparable to experimentally obtained values, whereas the rigid band approach yields negligible demagnetization, even when the microscopic spin-flip process is assumed to be instantaneous. This shows that rigid band structure calculations will never be in quantitative agreement with experiments, irrespective of the investigated microscopic scattering mechanism.
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Affiliation(s)
- A J Schellekens
- Department of Applied Physics, Center for NanoMaterials (cNM), Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
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16
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Haazen PPJ, Murè E, Franken JH, Lavrijsen R, Swagten HJM, Koopmans B. Domain wall depinning governed by the spin Hall effect. Nat Mater 2013; 12:299-303. [PMID: 23377291 DOI: 10.1038/nmat3553] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Accepted: 12/17/2012] [Indexed: 05/12/2023]
Abstract
Perpendicularly magnetized materials have attracted significant interest owing to their high anisotropy, which gives rise to extremely narrow, nanosized domain walls. As a result, the recently studied current-induced domain wall motion (CIDWM) in these materials promises to enable a new class of data, memory and logic devices. Here we propose the spin Hall effect as an alternative mechanism for CIDWM. We are able to carefully tune the net spin Hall current in depinning experiments on Pt/Co/Pt nanowires, offering unique control over CIDWM. Furthermore, we determine that the depinning efficiency is intimately related to the internal structure of the domain wall, which we control by the application of small fields along the nanowire. This manifestation of CIDWM offers an attractive degree of freedom for manipulating domain wall motion by charge currents, and sheds light on the existence of contradicting reports on CIDWM in perpendicularly magnetized materials.
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Affiliation(s)
- P P J Haazen
- Department of Applied Physics, Center for NanoMaterials and COBRA Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
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17
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Maroteaux G, Loos M, van der Sluis S, Koopmans B, Aarts E, van Gassen K, Geurts A, Largaespada DA, Spruijt BM, Stiedl O, Smit AB, Verhage M. High-throughput phenotyping of avoidance learning in mice discriminates different genotypes and identifies a novel gene. Genes Brain Behav 2012; 11:772-84. [PMID: 22846151 DOI: 10.1111/j.1601-183x.2012.00820.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Revised: 04/27/2012] [Accepted: 07/03/2012] [Indexed: 01/31/2023]
Abstract
Recognizing and avoiding aversive situations are central aspects of mammalian cognition. These abilities are essential for health and survival and are expected to have a prominent genetic basis. We modeled these abilities in eight common mouse inbred strains covering ∼75% of the species' natural variation and in gene-trap mice (>2000 mice), using an unsupervised, automated assay with an instrumented home cage (PhenoTyper) containing a shelter with two entrances. Mice visited this shelter for 20-1200 times/24 h and 71% of all mice developed a significant and often strong preference for one entrance. Subsequently, a mild aversive stimulus (shelter illumination) was automatically delivered when mice used their preferred entrance. Different genotypes developed different coping strategies. Firstly, the number of entries via the preferred entrance decreased in DBA/2J, C57BL/6J and 129S1/SvImJ, indicating that these genotypes associated one specific entrance with the aversive stimulus. Secondly, mice started sleeping outside (C57BL/6J, DBA/2J), indicating they associated the shelter, in general, with the aversive stimulus. Some mice showed no evidence for an association between the entrance and the aversive light, but did show markedly shorter shelter residence times in response to illumination, indicating they did perceive illumination as aversive. Finally, using this assay, we screened 43 different mutants, which yielded a novel gene, specc1/cytospinB. This mutant showed profound and specific delay in avoidance learning. Together, these data suggest that different genotypes express distinct learning and/or memory of associations between shelter entrance and aversive stimuli, and that specc1/cytospinB is involved in this aspect of cognition.
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Affiliation(s)
- G Maroteaux
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University Amsterdam and VU Medical Center, Amsterdam, The Netherlands
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18
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Franken JH, Swagten HJM, Koopmans B. Shift registers based on magnetic domain wall ratchets with perpendicular anisotropy. Nat Nanotechnol 2012; 7:499-503. [PMID: 22796743 DOI: 10.1038/nnano.2012.111] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Accepted: 06/01/2012] [Indexed: 06/01/2023]
Abstract
The movement of magnetic domain walls can be used to build a device known as a shift register, which has applications in memory and logic circuits. However, the application of magnetic domain wall shift registers has been hindered by geometrical restrictions, by randomness in domain wall displacement and by the need for high current densities or rotating magnetic fields. Here, we propose a new approach in which the energy landscape experienced by the domain walls is engineered to favour a unidirectional ratchet-like propagation. The domain walls are defined between domains with an out-of-plane (perpendicular) magnetization, which allows us to route domain walls along arbitrary in-plane paths using a time-varying applied magnetic field with fixed orientation. In addition, this ratchet-like motion causes the domain walls to lock to discrete positions along these paths, which is useful for digital devices. As a proof-of-principle experiment we demonstrate the continuous propagation of two domain walls along a closed-loop path in a platinum/cobalt/platinum strip.
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Affiliation(s)
- J H Franken
- Department of Applied Physics, Center for NanoMaterials, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
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19
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Franken JH, Hoeijmakers M, Swagten HJM, Koopmans B. Tunable resistivity of individual magnetic domain walls. Phys Rev Lett 2012; 108:037205. [PMID: 22400781 DOI: 10.1103/physrevlett.108.037205] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Indexed: 05/31/2023]
Abstract
Despite the relevance of current-induced magnetic domain wall (DW) motion for new spintronics applications, the exact details of the current-domain wall interaction are not yet understood. A property intimately related to this interaction is the intrinsic DW resistivity. Here, we investigate experimentally how the resistivity inside a DW depends on the wall width Δ, which is tuned using focused ion beam irradiation of Pt/Co/Pt strips. We observe the nucleation of individual DWs with Kerr microscopy, and measure resistance changes in real time. A 1/Δ(2) dependence of DW resistivity is found, compatible with Levy-Zhang theory. Also quantitative agreement with theory is found by taking full account of the current flowing through each individual layer inside the multilayer stack.
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Affiliation(s)
- J H Franken
- Department of Applied Physics, Center for NanoMaterials and COBRA Research Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
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20
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Heinen J, Hinzke D, Boulle O, Malinowski G, Swagten HJM, Koopmans B, Ulysse C, Faini G, Ocker B, Wrona J, Kläui M. Determination of the spin torque non-adiabaticity in perpendicularly magnetized nanowires. J Phys Condens Matter 2012; 24:024220. [PMID: 22172802 DOI: 10.1088/0953-8984/24/2/024220] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Novel nanofabrication methods and the discovery of an efficient manipulation of local magnetization based on spin polarized currents has generated a tremendous interest in the field of spintronics. The search for materials allowing for fast domain wall dynamics requires fundamental research into the effects involved (Oersted fields, adiabatic and non-adiabatic spin torque, Joule heating) and possibilities for a quantitative comparison. Theoretical descriptions reveal a material and geometry dependence of the non-adiabaticity factor β, which governs the domain wall velocity. Here, we present two independent approaches for determining β: (i) measuring the dependence of the dwell times for which a domain wall stays in a metastable pinning state on the injected current and (ii) the current-field equivalence approach. The comparison of the deduced β values highlights the problems of using one-dimensional models to describe two-dimensional dynamics and allows us to ascertain the reliability, robustness and limits of the approaches used.
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Affiliation(s)
- J Heinen
- Fachbereich Physik, Universität Konstanz, Konstanz, Germany
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21
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Kersten SP, Schellekens AJ, Koopmans B, Bobbert PA. Magnetic-field dependence of the electroluminescence of organic light-emitting diodes: a competition between exciton formation and spin mixing. Phys Rev Lett 2011; 106:197402. [PMID: 21668199 DOI: 10.1103/physrevlett.106.197402] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2010] [Indexed: 05/30/2023]
Abstract
We explore the magnetoelectroluminescence (MEL) of organic light-emitting diodes by evaluating the magnetic-field dependent fraction of singlet excitons formed. We use two- and multisite polaron-hopping models with spin mixing by hyperfine fields and different singlet and triplet exciton formation rates k(S) and k(T). A huge MEL is predicted when exciton formation is in competition with spin mixing and when k(T) is significantly larger than k(S). This competition also leads to a low-field structure in the MEL that is in agreement with recent experiments.
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Affiliation(s)
- S P Kersten
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
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22
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Kurnosikov O, Swagten HJM, Koopmans B. Internal electron diffraction from atomically ordered subsurface nanostructures in metals. Phys Rev Lett 2011; 106:196803. [PMID: 21668187 DOI: 10.1103/physrevlett.106.196803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2010] [Revised: 03/01/2011] [Indexed: 05/30/2023]
Abstract
We demonstrate that a part of interface at a subsurface nanocavity in Cu(110) can efficiently induce electron scattering back to the surface even if it is inclined with respect to the surface, if the condition for electron diffraction is fulfilled. This backscattering induces oscillations of electron local density of states at the surface versus electron energy. In agreement with our model calculations, the diffraction is assigned to a specific atomic structure at the interface, and is found to be significantly enhanced by focussing of electron waves for propagation along the [110] direction.
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Affiliation(s)
- O Kurnosikov
- Department of Applied Physics, cNM, Eindhoven University of Technology, 5600MB Eindhoven, The Netherlands
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23
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Wagemans W, Schellekens AJ, Kemper M, Bloom FL, Bobbert PA, Koopmans B. Spin-spin interactions in organic magnetoresistance probed by angle-dependent measurements. Phys Rev Lett 2011; 106:196802. [PMID: 21668186 DOI: 10.1103/physrevlett.106.196802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Indexed: 05/30/2023]
Abstract
The dependence of organic magnetoresistance (OMAR) on the orientation of the magnetic field has been investigated. In contrast with previous claims, a finite and systematic change in magnitude is observed when the orientation of the field is changed with respect to the sample. It is demonstrated that, to explain these effects, spin-spin interactions have to be included in the models previously suggested for OMAR. Dipole coupling and exchange coupling are introduced in combination with either an anisotropy of the orientation of the spin pairs or an anisotropy in the hyperfine fields.
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Affiliation(s)
- W Wagemans
- Department of Applied Physics, Center for NanoMaterials, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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Lavrijsen R, Córdoba R, Schoenaker FJ, Ellis TH, Barcones B, Kohlhepp JT, Swagten HJM, Koopmans B, De Teresa JM, Magén C, Ibarra MR, Trompenaars P, Mulders JJL. Fe:O:C grown by focused-electron-beam-induced deposition: magnetic and electric properties. Nanotechnology 2011; 22:025302. [PMID: 21135470 DOI: 10.1088/0957-4484/22/2/025302] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We systematically study the effect of oxygen content on the magneto-transport and microstructure of Fe:O:C nanowires deposited by focused-electron-beam-induced (FEBID) deposition. The Fe/O ratio can be varied with an Fe content varying between ∼ 50 and 80 at.% with overall low C content (≈16 ± 3 at.%) by adding H(2)O during the deposition while keeping the beam parameters constant as measured by energy dispersive x-ray (EDX) spectroscopy. The room-temperature magnetic properties for deposits with an Fe content of 66-71 at.% are investigated using the magneto-optical Kerr effect (MOKE) and electric magneto-transport measurements. The nanostructure of the deposits is investigated through cross-sectional high-resolution transmission electron microscopy (HRTEM) imaging, allowing us to link the observed magneto-resistance and resistivity to the transport mechanism in the deposits. These results demonstrate that functional magnetic nanostructures can be created, paving the way for new magnetic or even spintronics devices.
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Affiliation(s)
- R Lavrijsen
- Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands.
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25
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Koopmans B, Malinowski G, Dalla Longa F, Steiauf D, Fähnle M, Roth T, Cinchetti M, Aeschlimann M. Explaining the paradoxical diversity of ultrafast laser-induced demagnetization. Nat Mater 2010; 9:259-65. [PMID: 20010830 DOI: 10.1038/nmat2593] [Citation(s) in RCA: 223] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Accepted: 11/03/2009] [Indexed: 05/22/2023]
Abstract
Pulsed-laser-induced quenching of ferromagnetic order has intrigued researchers since pioneering works in the 1990s. It was reported that demagnetization in gadolinium proceeds within 100 ps, but three orders of magnitude faster in ferromagnetic transition metals such as nickel. Here we show that a model based on electron-phonon-mediated spin-flip scattering explains both timescales on equal footing. Our interpretation is supported by ab initio estimates of the spin-flip scattering probability, and experimental fluence dependencies are shown to agree perfectly with predictions. A phase diagram is constructed in which two classes of laser-induced magnetization dynamics can be distinguished, where the ratio of the Curie temperature to the atomic magnetic moment turns out to have a crucial role. We conclude that the ultrafast magnetization dynamics can be well described disregarding highly excited electronic states, merely considering the thermalized electron system.
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Affiliation(s)
- B Koopmans
- Department of Applied Physics, Center for NanoMaterials (cNM), Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
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26
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Schoonus JJHM, Lumens PGE, Wagemans W, Kohlhepp JT, Bobbert PA, Swagten HJM, Koopmans B. Magnetoresistance in hybrid organic spin valves at the onset of multiple-step tunneling. Phys Rev Lett 2009; 103:146601. [PMID: 19905590 DOI: 10.1103/physrevlett.103.146601] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2009] [Indexed: 05/28/2023]
Abstract
By combining experiments with simple model calculations, we obtain new insight in spin transport through hybrid, CoFeB/Al2O3(1.5 nm)/tris(8-hydroxyquinoline)aluminium (Alq3)/Co spin valves. We have measured the characteristic changes in the I-V behavior as well as the intrinsic loss of magnetoresistance at the onset of multiple-step tunneling. In the regime of multiple-step tunneling, under the condition of low hopping rates, spin precession in the presence of hyperfine coupling is conjectured to be the relevant source of spin relaxation. A quantitative analysis leads to the prediction of a symmetric magnetoresistance around zero magnetic field in addition to the hysteretic magnetoresistance curves, which are indeed observed in our experiments.
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Affiliation(s)
- J J H M Schoonus
- Department of Applied Physics, cNM, Eindhoven University of Technology, The Netherlands
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27
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Koopmans B, Pouwer F, de Bie RA, Leusink GL, Denollet JKL, Pop VJM. Associations between vascular co-morbidities and depression in insulin-naive diabetes patients: the DIAZOB Primary Care Diabetes study. Diabetologia 2009; 52:2056-63. [PMID: 19669635 PMCID: PMC2744805 DOI: 10.1007/s00125-009-1460-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Accepted: 06/16/2009] [Indexed: 12/02/2022]
Abstract
AIMS/HYPOTHESIS The aim of the study was to determine the prevalence of depression in insulin-naive diabetes patients and to investigate the associations between different forms of vascular co-morbidity and depression. METHODS Cross-sectional data were used from a primary-care sample of 1,269 insulin-naive (i.e. not using insulin therapy) diabetes patients participating in the DIAZOB Primary Care Diabetes study. Demographics, vascular co-morbidities, clinical and lifestyle characteristics, and psychosocial factors were assessed. Depression symptoms were measured with the Edinburgh Depression Scale, with a score >11 defined as depression. The chi (2) and Student's t tests were used to compare groups with and without vascular co-morbidities. Rates and odds ratios of depression were calculated for each vascular co-morbidity, with diabetes only as the reference group, correcting for age and sex. Single and multiple logistic regression analyses were performed to test a more comprehensive model regarding the likelihood of depression in diabetes. RESULTS The prevalence of depression was 11% in the total sample with little difference between the groups with and without any vascular co-morbidity (11.2% vs 10.0%). Single vascular co-morbidities were not associated with increased rates of depression. The final model predicting depression included: having multiple vascular co-morbidities compared with none; having less social support; having experienced a recent stressful life event; female sex; and being a smoker. CONCLUSIONS/INTERPRETATION Rates of depression in those with one additional vascular co-morbidity did not differ from patients with diabetes only. Vascular co-morbidities were only associated with higher depression scores in case of multiple co-morbidities.
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Affiliation(s)
- B. Koopmans
- Center of Research on Psychology in Somatic diseases (CoRPS), Department of Medical Psychology, Tilburg University, P.O. Box 90153, 5000 LE Tilburg, the Netherlands
| | - F. Pouwer
- Center of Research on Psychology in Somatic diseases (CoRPS), Department of Medical Psychology, Tilburg University, P.O. Box 90153, 5000 LE Tilburg, the Netherlands
| | - R. A. de Bie
- CAPHRI School, Department of Epidemiology, Maastricht University, Maastricht, the Netherlands
| | | | - J. K. L. Denollet
- Center of Research on Psychology in Somatic diseases (CoRPS), Department of Medical Psychology, Tilburg University, P.O. Box 90153, 5000 LE Tilburg, the Netherlands
| | - V. J. M. Pop
- Center of Research on Psychology in Somatic diseases (CoRPS), Department of Medical Psychology, Tilburg University, P.O. Box 90153, 5000 LE Tilburg, the Netherlands
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Bloom FL, Kemerink M, Wagemans W, Koopmans B. Sign inversion of magnetoresistance in space-charge limited organic devices. Phys Rev Lett 2009; 103:066601. [PMID: 19792591 DOI: 10.1103/physrevlett.103.066601] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Indexed: 05/28/2023]
Abstract
In this Letter, we explain the puzzling sign change of organic magnetoresistance in space-charge limited devices by device physics. We prove analytically and numerically that in the case of bipolar conduction with an Ohmic majority carrier and an injection limited minority carrier contact, a decrease in minority carrier mobility may give rise to an increase in the device current. It is shown that when the magnetic field acts to decrease the mobility of both carriers, a sign change in the magnetoconductivity as a function of applied bias may result. This behavior is in agreement with experimental observations.
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Affiliation(s)
- F L Bloom
- Department of Applied Physics, Center for NanoMaterials, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
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29
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Koopmans B, Andersen BL, Mørk NJ, Austad J, Suhonen R, Roders GA. Multicentre randomized double-blind study of Locoid Lipocream fatty cream twice daily versus Locoid Lipocream once daily and Locobase once daily. J DERMATOL TREAT 2009. [DOI: 10.3109/09546639509097161] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Bobbert PA, Wagemans W, van Oost FWA, Koopmans B, Wohlgenannt M. Theory for spin diffusion in disordered organic semiconductors. Phys Rev Lett 2009; 102:156604. [PMID: 19518664 DOI: 10.1103/physrevlett.102.156604] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2009] [Indexed: 05/27/2023]
Abstract
We present a theory for spin diffusion in disordered organic semiconductors, based on incoherent hopping of a charge carrier and coherent precession of its spin in an effective magnetic field, composed of the random hyperfine field of hydrogen nuclei and an applied magnetic field. From Monte Carlo simulations and an analysis of the waiting-time distribution of the carrier we predict a surprisingly weak temperature dependence, but a considerable magnetic-field dependence of the spin-diffusion length. We show that both predictions are in agreement with experiments on organic spin valves.
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Affiliation(s)
- P A Bobbert
- Department of Applied Physics, Technische Universiteit Eindhoven, 5600 MB Eindhoven, The Netherlands
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31
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Kurnosikov O, Nietsch JH, Sicot M, Swagten HJM, Koopmans B. Long-range electron interferences at a metal surface induced by buried nanocavities. Phys Rev Lett 2009; 102:066101. [PMID: 19257608 DOI: 10.1103/physrevlett.102.066101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Indexed: 05/27/2023]
Abstract
Apparent c(2x2) superstructures within the narrow beams of an interference pattern spreading in the 100 directions at the surface of Cu(001) are observed by scanning tunneling microscopy. These features are induced by electron scattering from Ar- and Ne-filled subsurface nanocavities. The beams originate from electron anisotropy resulting in focusing of bulk electrons. We developed a model providing a good agreement between simulations and experiments. Particularly, a simple explanation of the angular distribution for the interference pattern and the period in the superstructure is found.
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Affiliation(s)
- O Kurnosikov
- Department of Applied Physics, cNM, Eindhoven University of Technology, 5600MB Eindhoven, The Netherlands
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32
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Paluskar PV, Lavrijsen R, Sicot M, Kohlhepp JT, Swagten HJM, Koopmans B. Correlation between magnetism and spin-dependent transport in CoFeB alloys. Phys Rev Lett 2009; 102:016602. [PMID: 19257223 DOI: 10.1103/physrevlett.102.016602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2008] [Indexed: 05/27/2023]
Abstract
We report a correlation between the spin polarization of the tunneling electrons and the magnetic moment of amorphous CoFeB alloys. Such a correlation is surprising since the spin polarization of the tunneling electrons involves s-like electrons close to the Fermi level (E_{F}), while the magnetic moment mainly arises due to all the d electrons below E_{F}. We show that probing the s and d bands individually provides clear and crucial evidence for such a correlation to exist through s-d hybridization, and demonstrate the tunability of the electronic and magnetic properties of CoFeB alloys.
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Affiliation(s)
- P V Paluskar
- Department of Applied Physics, cNM, Eindhoven University of Technology, 5600 MB, The Netherlands
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33
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Boulle O, Kimling J, Warnicke P, Kläui M, Rüdiger U, Malinowski G, Swagten HJM, Koopmans B, Ulysse C, Faini G. Nonadiabatic spin transfer torque in high anisotropy magnetic nanowires with narrow domain walls. Phys Rev Lett 2008; 101:216601. [PMID: 19113434 DOI: 10.1103/physrevlett.101.216601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2008] [Indexed: 05/27/2023]
Abstract
Current induced domain wall (DW) depinning of a narrow DW in out-of-plane magnetized (Pt/Co)_{3}/Pt multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism.
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Affiliation(s)
- O Boulle
- Fachbereich Physik, Universität Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany
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34
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Schoonus JJHM, Bloom FL, Wagemans W, Swagten HJM, Koopmans B. Extremely large magnetoresistance in boron-doped silicon. Phys Rev Lett 2008; 100:127202. [PMID: 18517905 DOI: 10.1103/physrevlett.100.127202] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Indexed: 05/26/2023]
Abstract
Boron-doped Si-SiO2-Al structures are fabricated to study extremely large magnetoresistance (MR) effects. Current-voltage characteristics show a nonlinear behavior, dominated by an autocatalytic process of impact ionization. At low temperatures, the magnetic field postpones the onset of impact ionization to higher electric fields. This results in a symmetric positive MR of over 10,000% at 400 kA/m. Applying a magnetic field leads to an increase of the acceptor level compared to the valence band as deduced by admittance spectroscopy. A macroscopic transport model is introduced to describe how the MR is controlled by voltage, electrode spacing, and oxide thickness.
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Affiliation(s)
- J J H M Schoonus
- Department of Applied Physics, cNM, Eindhoven University of Technology, The Netherlands
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Paluskar PV, Attema JJ, de Wijs GA, Fiddy S, Snoeck E, Kohlhepp JT, Swagten HJM, de Groot RA, Koopmans B. Spin tunneling in junctions with disordered ferromagnets. Phys Rev Lett 2008; 100:057205. [PMID: 18352421 DOI: 10.1103/physrevlett.100.057205] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Indexed: 05/26/2023]
Abstract
We provide compelling evidence to establish that, contrary to one's elementary guess, the tunneling spin polarization (TSP) of amorphous CoFeB is larger than that of fcc CoFeB. First-principles atomic and electronic structure calculations reveal striking agreement between the measured TSP and the predicted s-electron spin polarization. Given the disordered structure of the ternary alloy, not only do these results strongly endorse our communal understanding of tunneling through AlO(x), but they also portray the key concepts that demand primary consideration in such complex systems.
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Affiliation(s)
- P V Paluskar
- Department of Applied Physics, cNM, Eindhoven University of Technology, The Netherlands.
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Bloom FL, Wagemans W, Kemerink M, Koopmans B. Separating positive and negative magnetoresistance in organic semiconductor devices. Phys Rev Lett 2007; 99:257201. [PMID: 18233553 DOI: 10.1103/physrevlett.99.257201] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2007] [Indexed: 05/25/2023]
Abstract
We study the transition between positive and negative organic magnetoresistance (OMAR) in tris-(8 hydroxyquinoline) aluminium (Alq_{3}), in order to identify the elementary mechanisms governing this phenomenon. We show how the sign of OMAR changes as function of the applied voltage and temperature. The transition from negative to positive magnetoresistance (MR) is found to be accompanied by an increase in slope of log(I) versus log(V). ac admittance measurements show this transition coincides with the onset of minority charge (hole) injection in the device. All these observations are consistent with two simultaneous contributions with opposite sign of MR, which may be assigned to holes and electrons having different magnetic field responses.
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Affiliation(s)
- F L Bloom
- Department of Applied Physics, Center for NanoMaterials, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
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Bobbert PA, Nguyen TD, van Oost FWA, Koopmans B, Wohlgenannt M. Bipolaron mechanism for organic magnetoresistance. Phys Rev Lett 2007; 99:216801. [PMID: 18233239 DOI: 10.1103/physrevlett.99.216801] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2007] [Indexed: 05/20/2023]
Abstract
We present a mechanism for the recently discovered magnetoresistance in disordered pi-conjugated materials, based on hopping of polarons and bipolaron formation, in the presence of the random hyperfine fields of the hydrogen nuclei and an external magnetic field. Within a simple model we describe the magnetic field dependence of the bipolaron density. Monte Carlo simulations including on-site and longer-range Coulomb repulsion show how this leads to positive and negative magnetoresistance. Depending on the branching ratio between bipolaron formation or dissociation and hopping rates, two different line shapes in excellent agreement with experiment are obtained.
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Affiliation(s)
- P A Bobbert
- Group Polymer Physics and Eindhoven Polymer Laboratories, Technische Universiteit Eindhoven, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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Schoonus JJHM, Kurnosikov O, Swagten HJM, Koopmans B, Geluk EJ, Karouta F, Van Roy W, Borghs G. Towards all-electrical spin injection and detection in GaAs. ACTA ACUST UNITED AC 2006. [DOI: 10.1002/pssc.200672818] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
We present a microscopic model that successfully explains the ultrafast equilibration of magnetic order in ferromagnetic metals at a time scale tau(M) of only a few hundred femtoseconds after pulsed laser excitation. It is found that tau(M) can be directly related to the so-called Gilbert damping factor sigma that describes damping of GHz precessional motion of the magnetization vector. Independent of the spin-scattering mechanism, an appealingly simple equation relating the two key parameters via the Curie temperature T(C) is derived, tau(M) approximately c(0)h/k(B)T(C)sigma, with h and k(B) the Planck and Boltzmann constants, respectively, and the prefactor c(0) approximately 1/4). We argue that phonon-mediated spin-flip scattering may contribute significantly to the sub-ps response.
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Affiliation(s)
- B Koopmans
- Department of Applied Physics, Center for NanoMaterials (cNM) Eindhoven University of Technology, The Netherlands.
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Van Kampen M, Jozsa C, Kohlhepp JT, LeClair P, Lagae L, De Jonge WJM, Koopmans B. All-optical probe of coherent spin waves. Phys Rev Lett 2002; 88:227201. [PMID: 12059451 DOI: 10.1103/physrevlett.88.227201] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2002] [Indexed: 05/23/2023]
Abstract
A novel, all-optical method to excite and detect spin waves in magnetic materials is presented. By exploiting the temperature dependence of the magnetic anisotropy, an ultrashort laser pulse is efficiently converted in a picosecond "anisotropy field" pulse that triggers a coherent precession of the magnetization. Recording the temporal evolution of the precessing spins by a time-delayed probe-pulse provides a quantitative method to study locally the magnetic anisotropy, as well as switching and damping phenomena in micromagnetic structures. Applications to nickel and permalloy ( Ni80Fe20) films are discussed, particularly showing the possibility to explore standing spin waves in thin films.
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Affiliation(s)
- M Van Kampen
- Department of Applied Physics, Center for NanoMaterials and COBRA Research Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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Abstract
Several magnetic and optical processes contribute to the magneto-optical response of nickel thin films after excitation by a femtosecond laser pulse. We achieved a first complete identification by explicitly measuring the time-resolved Kerr ellipticity and rotation, as well as its temperature and magnetic field dependence in epitaxially grown (111) and (001) oriented Cu/Ni/Cu wedges. The first hundreds of femtoseconds the response is dominated by state filling effects. The true demagnetization takes approximately 0.5-1 ps. At the longer (sub-ns) time scales the spins are found to precess in their anisotropy field. Simple and transparent models are introduced to substantiate our interpretation.
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Affiliation(s)
- B Koopmans
- Eindhoven University of Technology, Department of Applied Physics, COBRA Research Institute, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands
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Santos PV, Koopmans B, Esser N, Schmidt WG, Bechstedt F. Optical Properties of Ordered As Layers on InP(110) Surfaces. Phys Rev Lett 1996; 77:759-762. [PMID: 10062895 DOI: 10.1103/physrevlett.77.759] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Etchegoin P, Fainstein A, Sirenko AA, Koopmans B, Richards B, Santos PV, Cardona M, Totenmeyer K, Eberl K. Optics of multiple quantum wells uniaxially stressed along the growth axis. Phys Rev B Condens Matter 1996; 53:13662-13671. [PMID: 9983114 DOI: 10.1103/physrevb.53.13662] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Janner A, Eder R, Koopmans B, Jonkman HT, Sawatzky GA. Excitons in C60 studied by temperature-dependent optical second-harmonic generation. Phys Rev B Condens Matter 1995; 52:17158-17164. [PMID: 9981142 DOI: 10.1103/physrevb.52.17158] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Koopmans B, Koerkamp MG, Rasing T. Observation of large Kerr angles in the nonlinear optical response from magnetic multilayers. Phys Rev Lett 1995; 74:3692-3695. [PMID: 10058269 DOI: 10.1103/physrevlett.74.3692] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Koopmans B, Janner AM, Jonkman HT, Sawatzky GA. Strong bulk magnetic dipole induced second-harmonic generation from C60. Phys Rev Lett 1993; 71:3569-3572. [PMID: 10055010 DOI: 10.1103/physrevlett.71.3569] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Koopmans B, Anema A, Jonkman HT, Sawatzky GA. Resonant-optical-second-harmonic generation from thin C60 films. Phys Rev B Condens Matter 1993; 48:2759-2764. [PMID: 10008676 DOI: 10.1103/physrevb.48.2759] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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