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  • 1.
    Negi, Devendra Singh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Datta, Ranjan
    Jawaharlal Nehru Ctr Adv Sci Res, Int Ctr Mat Sci, Bangalore 560064, Karnataka, India;Jawaharlal Nehru Ctr Adv Sci Res, Chem & Phys Mat Unit, Bangalore 560064, Karnataka, India.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Defect driven spin state transition and the existence of half-metallicity in CoO2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 11, article id 115602Article in journal (Refereed)
    Abstract [en]

    We unveil the native defect induced high spin to low spin state transition in Co+3 and half- metallicity in CoO. First principles calculations unravel that, defect density holds a key role in dictating the spin-state transition in Co+3 ion in CoO, and introducing the half-metallicity. Charge transfer in the vicinity of vacancy plane favors the stabilization and coexistence of bivalent Co+2 and trivalent Co+3 ion in CoO. We propose that defect engineering could serve as a route to design the half metallicity in transition metal mono-oxides.

  • 2.
    Negi, Devendra Singh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Idrobo, Juan Carlos
    Ctr Nanophase Mat Sci, Oak Ridge Natl Lab, Oak Ridge, TN 37831 USA..
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Probing the localization of magnetic dichroism by atomic-size astigmatic and vortex electron beams2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 4019Article in journal (Refereed)
    Abstract [en]

    We report localization of a magnetic dichroic signal on atomic columns in electron magnetic circular dichroism ( EMCD), probed by beam distorted by four-fold astigmatism and electron vortex beam. With astigmatic probe, magnetic signal to noise ratio can be enhanced by blocking the intensity from the central part of probe. However, the simulations show that for atomic resolution magnetic measurements, vortex beam is a more effective probe, with much higher magnetic signal to noise ratio. For all considered beam shapes, the optimal SNR constrains the signal detection at low collection angles of approximately 6-8 mrad. Irrespective of the material thickness, the magnetic signal remains strongly localized within the probed atomic column with vortex beam, whereas for astigmatic probes, the magnetic signal originates mostly from the nearest neighbor atomic columns. Due to excellent signal localization at probing individual atomic columns, vortex beams are predicted to be a strong candidate for studying the crystal site specific magnetic properties, magnetic properties at interfaces, or magnetism arising from individual atomic impurities.

  • 3.
    Negi, Devendra Singh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jones, Lewys
    Ctr Res Adapt Nanostruct & Nanodevices CRANN, Adv Microscopy Lab, Dublin 2, Ireland;Trinity Coll Dublin, Sch Phys, Dublin 2, Ireland.
    Idrobo, Juan-Carlos
    Oak Ridge Natl Lab, Ctr Nanophase Mat Sci, POB 2009, Oak Ridge, TN 37831 USA.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Proposal for a three-dimensional magnetic measurement method with nanometer-scale depth resolution2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 17, article id 174409Article in journal (Refereed)
    Abstract [en]

    We propose a magnetic measurement method based on combining depth sectioning and electron magnetic circular dichroism in scanning transmission electron microscopy. Electron vortex beams with large convergence angles, as those achievable in current state-of-the-art aberration correctors, could produce atomic lateral resolution and depth resolution below 2 nm.

  • 4.
    Negi, Devendra Singh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Spiegelberg, Jakob
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Muto, Shunsuke
    Nagoya Univ, Elect Nanoscopy Sect, Adv Measurement Technol Ctr, Inst Mat & Syst Sustainabil,Chikusa Ku, Furo Cho, Nagoya, Aichi 4648603, Japan.
    Thersleff, Thomas
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius Vag 16C, S-10691 Stockholm, Sweden.
    Ohtsuka, Masahiro
    Nagoya Univ, Grad Sch Engn, Dept Mat Phys, Chikusa Ku, Furo Cho, Nagoya, Aichi 4648603, Japan.
    Schonstrom, Linus
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius Vag 16C, S-10691 Stockholm, Sweden.
    Tatsumi, Kazuyoshi
    Nagoya Univ, Inst Mat & Syst Sustainabil, Adv Measurement Technol Ctr, Chikusa Ku, Nagoya, Aichi 4648603, Japan.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Proposal for Measuring Magnetism with Patterned Apertures in a Transmission Electron Microscope2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, no 3, article id 037201Article in journal (Refereed)
    Abstract [en]

    We propose a magnetic measurement method utilizing a patterned postsample aperture in a transmission electron microscope. While utilizing electron magnetic circular dichroism, the method circumvents previous needs to shape the electron probe to an electron vortex beam or astigmatic beam. The method can be implemented in standard scanning transmission electron microscopes by replacing the spectrometer entrance aperture with a specially shaped aperture, hereafter called a ventilator aperture. The proposed setup is expected to work across the whole range of beam sizes-from wide parallel beams down to atomic resolution magnetic spectrum imaging.

  • 5.
    Negi, Devendra Singh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Max Planck Inst Solid State Res, Stuttgart Ctr Electron Microscopy, Heisenbergstr 1, D-70569 Stuttgart, Germany.
    Zeiger, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jones, Lewys
    CRANN, Adv Microscopy Lab, Dublin 2, Ireland;Trinity Coll Dublin, Sch Phys, Dublin 2, Ireland.
    Idrobo, Juan-Carlos
    Oak Ridge Natl Lab, Ctr Nanophase Mat Sci, Oak Ridge, TN 37831 USA.
    van Aken, Peter A.
    Max Planck Inst Solid State Res, Stuttgart Ctr Electron Microscopy, Heisenbergstr 1, D-70569 Stuttgart, Germany.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Prospect for detecting magnetism of a single impurity atom using electron magnetic chiral dichroism2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 10, article id 104434Article in journal (Refereed)
    Abstract [en]

    Dopants, even single atoms, can influence the electrical and magnetic properties of materials. Here we demonstrate the opportunity for detecting the magnetic response of an embedded magnetic impurity in a nonmagnetic host material. We combine a depth sectioning approach with electron magnetic circular dichroism in scanning transmission electron microscopy to compute the depth-resolved magnetic inelastic-scattering cross section of single Co impurity buried in the host crystal of GaAs. Our calculations suggest that the magnetic dichroic signal intensity is sensitive to the depth and lateral position of the electron probe relative to the magnetic impurity. Additionally, a more precise dichroic signal localization can be achieved via choosing higher-collection-angle (beta) apertures. Quantitative evaluation of the inelastic-scattering cross section and signal-to-noise ratio indicates that the magnetic signal from a single Co atom is on the verge of being detectable with today's state-of-the-art instrumentation.

  • 6.
    Schneider, Sebastian
    et al.
    IFW Dresden, Inst Metall Mat, Helmholtzstr 20, D-01069 Dresden, Germany;Tech Univ Dresden, Inst Festkorper & Mat Phys, D-01062 Dresden, Germany.
    Negi, Devendra Singh
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stolt, Matthew J.
    Univ Wisconsin, Dept Chem, 1101 Univ Ave, Madison, WI 53706 USA.
    Jin, Song
    Univ Wisconsin, Dept Chem, 1101 Univ Ave, Madison, WI 53706 USA.
    Spiegelberg, Jakob
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pohl, Darius
    IFW Dresden, Inst Metall Mat, Helmholtzstr 20, D-01069 Dresden, Germany;Tech Univ Dresden, Dresden Ctr Nanoanal, D-01062 Dresden, Germany.
    Rellinghaus, Bernd
    IFW Dresden, Inst Metall Mat, Helmholtzstr 20, D-01069 Dresden, Germany;Tech Univ Dresden, Dresden Ctr Nanoanal, D-01062 Dresden, Germany.
    Goennenwein, Sebastian T. B.
    Tech Univ Dresden, Inst Festkorper & Mat Phys, D-01062 Dresden, Germany;Tech Univ Dresden, Ctr Transport & Devices Emergent Mat, D-01062 Dresden, Germany.
    Nielsch, Kornelius
    IFW Dresden, Inst Metall Mat, Helmholtzstr 20, D-01069 Dresden, Germany;Tech Univ Dresden, Inst Mat Sci, Hehnholtzstr 7, D-01069 Dresden, Germany.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. IFW Dresden, Inst Metall Mat, Helmholtzstr 20, D-01069 Dresden, Germany.
    Simple method for optimization of classical electron magnetic circular dichroism measurements: The role of structure factor and extinction distances2018In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 11, article id 113801Article in journal (Refereed)
    Abstract [en]

    Electron magnetic circular dichroism (EMCD), the electron wave analog of x-ray magnetic circular dichroism (XMCD), allows for the element specific measurement of the spin and orbital magnetic moments with up to nanometer resolution. However, due to dynamical diffraction effects, the signal-to-noise ratios of EMCD spectra are often very low. We describe a simple set of rules, how to set up a geometry for a classical EMCD experiment on an arbitrary crystal structure to get a maximum dichroic signal. The procedure is based on an evaluation of the structure factor and extinction distances. Proof-of-concept simulations and experiments on a FeGe crystal present a successful test of these guidelines.

1 - 6 of 6
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