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Negi, Devendra Singh
Publications (6 of 6) Show all publications
Negi, D. S., Datta, R. & Rusz, J. (2019). Defect driven spin state transition and the existence of half-metallicity in CoO. Journal of Physics: Condensed Matter, 31(11), Article ID 115602.
Open this publication in new window or tab >>Defect driven spin state transition and the existence of half-metallicity in CoO
2019 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 11, article id 115602Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2019
Keywords
half-metallicty, transition metal oxides, spin state transition
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-376709 (URN)10.1088/1361-648X/aafd11 (DOI)000456850300002 ()30625423 (PubMedID)
Funder
Swedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyCarl Tryggers foundation Swedish National Infrastructure for Computing (SNIC)
Available from: 2019-02-13 Created: 2019-02-13 Last updated: 2019-02-13Bibliographically approved
Negi, D. S., Spiegelberg, J., Muto, S., Thersleff, T., Ohtsuka, M., Schonstrom, L., . . . Rusz, J. (2019). Proposal for Measuring Magnetism with Patterned Apertures in a Transmission Electron Microscope. Physical Review Letters, 122(3), Article ID 037201.
Open this publication in new window or tab >>Proposal for Measuring Magnetism with Patterned Apertures in a Transmission Electron Microscope
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2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, no 3, article id 037201Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-376816 (URN)10.1103/PhysRevLett.122.037201 (DOI)000456782500011 ()
Funder
Swedish Research Council, 2016-05113Knut and Alice Wallenberg Foundation, 3DEM-NATUR 2012.0112Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyCarl Tryggers foundation
Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-02-19Bibliographically approved
Negi, D. S., Zeiger, P., Jones, L., Idrobo, J.-C., van Aken, P. A. & Rusz, J. (2019). Prospect for detecting magnetism of a single impurity atom using electron magnetic chiral dichroism. Physical Review B, 100(10), Article ID 104434.
Open this publication in new window or tab >>Prospect for detecting magnetism of a single impurity atom using electron magnetic chiral dichroism
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 10, article id 104434Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-395834 (URN)10.1103/PhysRevB.100.104434 (DOI)000488252600004 ()
Funder
Swedish Research Council, 2017-04026Swedish National Infrastructure for Computing (SNIC)EU, Horizon 2020, 823717 ESTEEM3Göran Gustafsson Foundation for Research in Natural Sciences and Medicine
Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved
Negi, D. S., Idrobo, J. C. & Rusz, J. (2018). Probing the localization of magnetic dichroism by atomic-size astigmatic and vortex electron beams. Scientific Reports, 8, Article ID 4019.
Open this publication in new window or tab >>Probing the localization of magnetic dichroism by atomic-size astigmatic and vortex electron beams
2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 4019Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-350288 (URN)10.1038/s41598-018-22234-8 (DOI)000426540800052 ()29507317 (PubMedID)
Funder
Swedish Research CouncilGöran Gustafsson Foundation for Research in Natural Sciences and MedicineCarl Tryggers foundation
Available from: 2018-05-09 Created: 2018-05-09 Last updated: 2018-05-09Bibliographically approved
Negi, D. S., Jones, L., Idrobo, J.-C. & Rusz, J. (2018). Proposal for a three-dimensional magnetic measurement method with nanometer-scale depth resolution. Physical Review B, 98(17), Article ID 174409.
Open this publication in new window or tab >>Proposal for a three-dimensional magnetic measurement method with nanometer-scale depth resolution
2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 17, article id 174409Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-369392 (URN)10.1103/PhysRevB.98.174409 (DOI)000449384600003 ()
Funder
Swedish Research Council
Available from: 2019-01-14 Created: 2019-01-14 Last updated: 2019-01-14Bibliographically approved
Schneider, S., Negi, D. S., Stolt, M. J., Jin, S., Spiegelberg, J., Pohl, D., . . . Rusz, J. (2018). Simple method for optimization of classical electron magnetic circular dichroism measurements: The role of structure factor and extinction distances. PHYSICAL REVIEW MATERIALS, 2(11), Article ID 113801.
Open this publication in new window or tab >>Simple method for optimization of classical electron magnetic circular dichroism measurements: The role of structure factor and extinction distances
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2018 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 11, article id 113801Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-371497 (URN)10.1103/PhysRevMaterials.2.113801 (DOI)000450572400001 ()
Funder
Swedish Research CouncilCarl Tryggers foundation Göran Gustafsson Foundation for Research in Natural Sciences and Medicine
Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-01-07Bibliographically approved
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