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Publications (10 of 218) Show all publications
Vovusha, H., Amorim, R. G., Scheicher, R. H. & Sanyal, B. (2018). Controlling the orientation of nucleobases by dipole moment interaction with graphene/h-BN interfaces. RSC Advances, 8(12), 6527-6531
Open this publication in new window or tab >>Controlling the orientation of nucleobases by dipole moment interaction with graphene/h-BN interfaces
2018 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 8, no 12, p. 6527-6531Article in journal (Refereed) Published
Abstract [en]

The interfaces in 2D hybrids of graphene and h-BN provide interesting possibilities of adsorbing and manipulating atomic and molecular entities. In this paper, with the aid of density functional theory, we demonstrate the adsorption characteristics of DNA nucleobases at different interfaces of 2D hybrid nanoflakes of graphene and h-BN. The interfaces provide stronger binding to the nucleobases in comparison to pure graphene and h-BN nanoflakes. It is also revealed that the individual dipole moments of the nucleobases and nanoflakes dictate the orientation of the nucleobases at the interfaces of the hybrid structures. The results of our study point towards a possible route to selectively control the orientation of individual molecules in biosensors.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-347655 (URN)10.1039/c7ra11664k (DOI)000425034000041 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilCarl Tryggers foundation
Available from: 2018-04-06 Created: 2018-04-06 Last updated: 2018-04-06Bibliographically approved
Autieri, C. & Sanyal, B. (2017). A systematic study of 4d and 5d transition metal mediated exchange coupling between Fe and Gd nanolaminates. Journal of Physics: Condensed Matter, 29(46), Article ID 465802.
Open this publication in new window or tab >>A systematic study of 4d and 5d transition metal mediated exchange coupling between Fe and Gd nanolaminates
2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 46, article id 465802Article in journal (Refereed) Published
Abstract [en]

We present a systematic study of the magnetic coupling between iron and gadolinium layers intermediated by 4d and 5d transition metals using density functional theory. We demonstrate that it is possible to find a magnetic coupling for most of them. In particular, for the early transition metals (d(1), d(2), d(3) and d(4)), a ferromagnetic coupling occurs even stronger than the 3d interlayers. Atomic size and the electronic configuration of the transition metals are crucial for the nature of the coupling. All the open shell transition metals present induced magnetic moments. By increasing the number of interlayers, an oscillating behavior in the magnetic coupling was found and the magnetic coupling goes to zero beyond four spacer layers. Using Monte Carlo simulations, we demonstrate that the interlayer strongly enhances the critical temperature in the Gd layers closest to the interface.

Keyword
magnetism, interface, high saturation magnetisation
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-340682 (URN)10.1088/1361-648X/aa8f1e (DOI)000413571000001 ()29057756 (PubMedID)
Funder
Swedish National Infrastructure for Computing (SNIC)
Available from: 2018-02-05 Created: 2018-02-05 Last updated: 2018-02-05Bibliographically approved
Hausmann, S., Ye, J., Aoki, T., Zheng, J.-G., Stahn, J., Bern, F., . . . Paul, A. (2017). Atomic-scale engineering of ferroelectric-ferromagnetic interfaces of epitaxial perovskite films for functional properties. Scientific Reports, 7, Article ID 10734.
Open this publication in new window or tab >>Atomic-scale engineering of ferroelectric-ferromagnetic interfaces of epitaxial perovskite films for functional properties
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 10734Article in journal (Refereed) Published
Abstract [en]

Besides epitaxial mismatch that can be accommodated by lattice distortions and/or octahedral rotations, ferroelectric-ferromagnetic interfaces are affected by symmetry mismatch and subsequent magnetic ordering. Here, we have investigated La-0.67 Sr-0.33 MnO3 (LSMO) samples with varying underlying unit cells (uc) of BaTiO3 (BTO) layer on (001) and (110) oriented substrates in order to elucidate the role of symmetry mismatch. Lattice mismatch for 3 uc of BTO and symmetry mismatch for 10 uc of BTO, both associated with local MnO6 octahedral distortions of the (001) LSMO within the first few uc, are revealed by scanning transmission electron microscopy. Interestingly, we find exchange bias along the in-plane [110]/[100] directions only for the (001) oriented samples. Polarized neutron reflectivity measurements confirm the existence of a layer with zero net moment only within (001) oriented samples. First principle density functional calculations show that even though the bulk ground state of LSMO is ferromagnetic, a large lattice constant together with an excess of La can stabilize an antiferromagnetic LaMnO3-type phase at the interface region and explain the experimentally observed exchange bias. Atomic scale tuning of MnO6 octahedra can thus be made possible via symmetry mismatch at heteroepitaxial interfaces. This aspect can act as a vital parameter for structure-driven control of physical properties.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2017
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-335394 (URN)10.1038/s41598-017-10194-4 (DOI)000409439900152 ()28878313 (PubMedID)
Funder
Carl Tryggers foundation , CTS 12:419, 13:413
Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2018-03-22Bibliographically approved
Li, L., Kong, X., Leenaerts, O., Chen, X., Sanyal, B. & Peeters, F. M. (2017). Carbon-rich carbon nitride monolayers with Dirac cones: Dumbbell C4N. Carbon, 118, 285-290
Open this publication in new window or tab >>Carbon-rich carbon nitride monolayers with Dirac cones: Dumbbell C4N
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2017 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 118, p. 285-290Article in journal (Refereed) Published
Abstract [en]

Two-dimensional (2D) carbon nitride materials play an important role in energy-harvesting, energy-storage and environmental applications. Recently, a new carbon nitride, 2D polyaniline (C3N) was proposed [PNAS 113 (2016) 7414-7419]. Based on the structure model of this C3N monolayer, we propose two new carbon nitride monolayers, named dumbbell (DB) C4N-I and C4N-II. Using first-principles calculations, we systematically study the structure, stability, and band structure of these two materials. In contrast to other carbon nitride monolayers, the orbital hybridization of the C/N atoms in the DB C4N monolayers is sp(3). Remarkably, the band structures of the two DB C4N monolayers have a Dirac cone at the K point and their Fermi velocities (2.6/2.4 x 10(5) m/s) are comparable to that of graphene. This makes them promising materials for applications in high-speed electronic devices. Using a tight-binding model, we explain the origin of the Dirac cone.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-323753 (URN)10.1016/j.carbon.2017.03.045 (DOI)000401120800033 ()
Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2017-06-13Bibliographically approved
Ivanov, S. A., Bush, A. A., Ritter, C., Behtin, M. A., Cherepanov, V. M., Autieri, C., . . . Mathieu, R. (2017). Evolution of the structural and multiferroic properties of PbFe2/3W1/3O3 ceramics upon Mn-doping. Materials Chemistry and Physics, 187, 218-232
Open this publication in new window or tab >>Evolution of the structural and multiferroic properties of PbFe2/3W1/3O3 ceramics upon Mn-doping
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2017 (English)In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 187, p. 218-232Article in journal (Refereed) Published
Abstract [en]

The perovskite system Pb(Fe1-xMnx)(2/3)W1/3O3 (0 <= x <= 1, PFMWO) has been prepared by conventional solid-state reaction under different sintering conditions. Structures and phase composition as well as thermal, magnetic and dielectric properties of the compounds have been systematically investigated experimentally and by first-principles density functional calculations. A clean perovskite phase is established at room temperature for compositions 0 <= x <= 0.4. Rietveld refinements of X-ray and neutron powder diffraction patterns demonstrate that the compounds crystallize in space group Pm-3m (0 <= x <= 0.4). The degree of ordering of the Fe and W/Mn cations was found to depend on the concentration of Mn. First-principles calculations suggest that the structural properties of PFMWO are strongly influenced by the Jahn Teller effect. The PFMWO compounds behave as relaxor ferroelectrics at weak Mn-doping with a dielectric constant that rapidly decreases with increasing Mn content. A low temperature antiferromagnetic G-type order with propagation vector k = (1/2,1/2,1/2) is derived from neutron powder diffraction data for the samples with x <= 0.4. However with increasing doping concentration, the magnetic order is perturbed. First principles calculations show that the dominant exchange coupling is antiferromagnetic and occurs between nearest neighbor Fe atoms. When the system is doped with Mn, a relatively weak ferromagnetic (FM) interaction between Fe and Mn atoms emerges. However, due to the presence of this FM interaction, the correlation length of the magnetic order is greatly shortened already at rather low doping levels.

Keyword
Oxides, Dielectric properties, Magnetic properties, Magnetic structures
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-316943 (URN)10.1016/j.matchemphys.2016.12.003 (DOI)000392786900026 ()
Funder
Swedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Knut and Alice Wallenberg FoundationCarl Tryggers foundation , CTS 12:419 13:413
Available from: 2017-03-09 Created: 2017-03-09 Last updated: 2017-11-29Bibliographically approved
Keshavarz, S., Kvashnin, Y. O., Rodrigues, D. C. M., Pereiro, M., Di Marco, I., Autieri, C., . . . Eriksson, O. (2017). Exchange interactions of CaMnO3 in the bulk and at the surface. Physical Review B Condensed Matter, 95, Article ID 115120.
Open this publication in new window or tab >>Exchange interactions of CaMnO3 in the bulk and at the surface
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2017 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 95, article id 115120Article in journal (Refereed) Published
Abstract [en]

We present electronic and magnetic properties of CaMnO3 (CMO) as obtained from ab initio calculations. We identify the preferable magnetic order by means of density functional theory plus Hubbard U calculations and extract the effective exchange parameters (Jij ' s) using the magnetic force theorem. We find that the effects of geometrical relaxation at the surface as well as the change of crystal field are very strong and are able to influence the lower-energymagnetic configuration. In particular, our analysis reveals that the exchange interaction between the Mn atoms belonging to the surface and the subsurface layers is very sensitive to the structural changes. An earlier study [A. Filippetti and W. E. Pickett, Phys. Rev. Lett. 83, 4184 (1999)] suggested that this coupling is ferromagnetic and gives rise to the spin-flip (SF) process on the surface of CMO. In our work, we confirm their finding for an unrelaxed geometry, but once the structural relaxations are taken into account, this exchange coupling changes its sign. Thus, we suggest that the surface of CMO should have the same G-type antiferromagnetic order as in the bulk. Finally, we show that the suggested SF can be induced in the system by introducing an excess of electrons.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-319934 (URN)10.1103/PhysRevB.95.115120 (DOI)000396008300003 ()
Funder
Swedish Research CouncileSSENCE - An eScience CollaborationKnut and Alice Wallenberg Foundation
Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2017-11-29Bibliographically approved
Autieri, C., Bouhon, A. & Sanyal, B. (2017). Gap opening and large spin–orbit splitting in MX2 (M = Mo,W; X = S,Se,Te) from the interplay between crystal field and hybridisations: insights from ab-initio theory. Philosophical Magazine, 97(35), 3381-3395
Open this publication in new window or tab >>Gap opening and large spin–orbit splitting in MX2 (M = Mo,W; X = S,Se,Te) from the interplay between crystal field and hybridisations: insights from ab-initio theory
2017 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 97, no 35, p. 3381-3395Article in journal (Refereed) Published
Abstract [en]

By means of first-principles density functional calculations, we study the maximally localised Wannier functions for the 2D transition metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te). We have found that part of the energy gap is opened by the crystal field splitting induced by the X-2-like atoms. The inversion of the band character between the Gamma and the K points of the Brillouin zone is due to the M-M hybridisation. The consequence of this inversion is the closure of the gap in absence of the M-X hybridisation. The M-X hybridisation is the only one that tends to open the gap at every k-point. It is found that the change in the M-X and M-M hybridisation is the main responsible for the difference in the gap between the different dichalcogenide materials. The inversion of the bands gives rise to different spinorbit splitting at Gamma and K point in the valence band. The different character of the gap at Gamma and K point offers the chance to manipulate the semiconducting properties of these compounds. For a bilayer system, the hybridisation between the out-of-plane orbitals and the hybridisation between the in-plane orbitals split the valence band respectively at the Gamma and K point. The splitting in the valence band is opened also without spin-orbit coupling and occurs due to the M-M and X-X hybridisation between the two monolayers. The transition from direct to indirect band gap is governed by the hybridisation between out-of-plane orbitals of different layers and in-plane orbitals of different layers.

Keyword
Nanostructured semiconductors, tight-binding Hamiltonians, strained layers
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-339513 (URN)10.1080/14786435.2017.1383634 (DOI)000418938700005 ()
Available from: 2018-01-19 Created: 2018-01-19 Last updated: 2018-01-19Bibliographically approved
Chimata, R., Delczeg-Czirjak, E. K., Szilva, A., Cardias, R., Kvashnin, Y., Pereiro, M., . . . Eriksson, O. (2017). Magnetism and ultrafast magnetization dynamics of Co and CoMn alloys at finite temperature. Physical review B, 95(21), Article ID 214417.
Open this publication in new window or tab >>Magnetism and ultrafast magnetization dynamics of Co and CoMn alloys at finite temperature
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2017 (English)In: Physical review B, ISSN 2469-9950, Vol. 95, no 21, article id 214417Article in journal (Refereed) Published
Abstract [en]

Temperature-dependent magnetic experiments such as pump-probe measurements generated by a pulsed laser have become a crucial technique for switching the magnetization in the picosecond time scale. Apart from having practical implications on the magnetic storage technology, the research field of ultrafast magnetization poses also fundamental physical questions. To correctly describe the time evolution of the atomic magnetic moments under the influence of a temperature-dependent laser pulse, it remains crucial to know if the magnetic material under investigation has magnetic excitation spectrum that is more or less dependent on the magnetic configuration, e.g., as reflected by the temperature dependence of the exchange interactions. In this paper, we demonstrate from first-principles theory that the magnetic excitation spectra in Co in fcc, bcc, and hcp structures are nearly identical in a wide range of noncollinear magnetic configurations. This is a curious result of a balance between the size of the magnetic moments and the strength of the Heisenberg exchange interactions, that in themselves vary with configuration, but put together in an effective spin Hamiltonian results in a configuration-independent effective model. We have used such a Hamiltonian, together with ab initio calculated damping parameters, to investigate the magnon dispersion relationship as well as ultrafast magnetization dynamics of Co and Co-rich CoMn alloys.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-308321 (URN)10.1103/PhysRevB.95.214417 (DOI)000404015400003 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2013.0020, 2012.0031StandUp
Available from: 2016-11-24 Created: 2016-11-24 Last updated: 2018-04-07Bibliographically approved
Kundu, A., Ghosh, S., Banerjee, R., Ghosh, S. & Sanyal, B. (2017). New quaternary half-metallic ferromagnets with large Curie temperatures. Scientific Reports, 7, Article ID 1803.
Open this publication in new window or tab >>New quaternary half-metallic ferromagnets with large Curie temperatures
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 1803Article in journal (Refereed) Published
Abstract [en]

New magnetic materials with high Curie temperatures for spintronic applications are perpetually sought for. In this paper, we present an ab initio study of the structural, electronic and magnetic properties of Quaternary Heusler compounds CoX'Y'Si where X' is a transition metal with 4d electrons and Y' is either Fe or Mn. We find five new half-metallic ferromagnets with spin polarisation nearly 100% with very high Curie temperatures. The variation of Curie temperatures as a function of valence electrons can be understood from the calculated inter-atomic exchange interaction parameters. We also identify a few other compounds, which could be potential half-metals with suitable application of pressure or with controlled doping. Our results reveal that the half-metallicity in these compounds is intricately related to the arrangements of the magnetic atoms in the Heusler lattice and hence, the interatomic exchange interactions between the moments. The trends in the atomic arrangements, total and local magnetic moments, interatomic magnetic exchange interactions and Curie temperatures are discussed with fundamental insights.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-325329 (URN)10.1038/s41598-017-01782-5 (DOI)000400959000070 ()28496114 (PubMedID)
Available from: 2017-06-29 Created: 2017-06-29 Last updated: 2017-06-29Bibliographically approved
Shibuya, T., Yasuoka, K., Mirbt, S. & Sanyal, B. (2017). Subsurface Polaron Concentration As a Factor in the Chemistry of Reduced TiO2 (110) Surfaces. The Journal of Physical Chemistry C, 121(21), 11325-11334
Open this publication in new window or tab >>Subsurface Polaron Concentration As a Factor in the Chemistry of Reduced TiO2 (110) Surfaces
2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 21, p. 11325-11334Article in journal (Refereed) Published
Abstract [en]

Surface reactivity of rutile TiO2 (110) surfaces has long been ascribed to bridging oxygen vacancies (V-o), but recently, excess electrons introduced by donor defects are being considered as the main players. However, the spatial distribution of them is not yet clear due to difficulties in interpreting filled state images of scanning tunneling microscopy (STM). In this study, several different images available in the literature are consistently interpreted using density functional theory (DFT). The key factors are polarons in the second layer below Ti-sc row (Tisc-2nd polarons) and a temperature dependence of their concentration. Bright blobs in the experimental images are interpreted as Tisc-2nd polarons. At 78 K, their concentration reaches 33.3% ML, where 1 ML is defined as the density of (1 x 1) unit cells, regardless of v(o) coverage. In contrast, at 5 K, it is twice the Vo coverage. This discrepancy is understood by the ionization of donor defects other than V-o, most probably subsurface Ti interstitials, and subsequent diffusion of polarons to Tisc-2nd sites at high temperature. This mechanism explains seemingly contradicting reports on oxygen chemisorption on this surface, which suggests that the so-called oxygen-vacancy model needs to be modified at temperature above at least 78 K.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-327240 (URN)10.1021/acs.jpcc.7b00935 (DOI)000402775200036 ()
Available from: 2017-08-08 Created: 2017-08-08 Last updated: 2017-08-08Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-3687-4223

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