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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
Samanta, S., Raghunathan, D., Mukherjee, S. & Sanyal, B. (2018). Dependence of homo-lumo gap of DNA base pair steps on twist angle: A density fuctional approach. Journal of biological systems, 26(1), 23-40
Open this publication in new window or tab >>Dependence of homo-lumo gap of DNA base pair steps on twist angle: A density fuctional approach
2018 (English)In: Journal of biological systems, ISSN 0218-3390, Vol. 26, no 1, p. 23-40Article in journal (Refereed) Published
Abstract [en]

Electronic structure calculations of all 10 unique base pair (bp) steps have been calculated to study the interaction energies of the bp steps, density of states (DOS), projected density of states (pDOS) using the density functional theory (DFT). Plane wave basis with ultrasoft pseudo-potential method has been used within the local density approximation (LDA) for the exchange correlation functional. Electron densities of the bp steps corresponding to HOMO and LUMO level have been calculated to understand the difference in stacking energies of the bp steps. The variation of HOMO-LUMO gap (g) of all possible bp steps on twist angle has been studied. We have observed that out of the 10 bp steps, 4 purine-purine bp steps (d(AA), d(GG), d(AG) and d(GA)), show significant variation of g on twist angle. The observed variation on twist angle of d(AA) bp step has been explained by the calculated DOS and electron densities.

Place, publisher, year, edition, pages
WORLD SCIENTIFIC PUBL CO PTE LTD, 2018
Keywords
DNA Base Pair Step, Stacking Energy, Density of States, HOMO-LUMO Gap, DFT Calculation
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-351750 (URN)10.1142/S021833901850002X (DOI)000429222700002 ()
Available from: 2018-06-04 Created: 2018-06-04 Last updated: 2018-06-04Bibliographically approved
Paul, S., Iusan, D., Thunström, P., Kvashnin, Y., Hellsvik, J., Pereiro, M., . . . Eriksson, O. (2018). Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory. Physical Review B, 97(12), Article ID 125120.
Open this publication in new window or tab >>Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125120Article in journal (Refereed) Published
Abstract [en]

Using the local density approximation plus dynamical mean-field theory (LDA+DMFT), we have computed the valence-band photoelectron spectra and magnetic excitation spectra of BiFeO3, one of the most studied multiferroics. Within the DMFT approach, the local impurity problem is tackled by the exact diagonalization solver. The solution of the impurity problem within the LDA+DMFT method for the paramagnetic and magnetically ordered phases produces result in agreement with the experimental data on electronic and magnetic structures. For comparison, we also present results obtained by the LDA+U approach which is commonly used to compute the physical properties of this compound. Our LDA+DMFT derived electronic spectra match adequately with the experimental hard x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy for Fe 3d states, whereas the LDA+U method fails to capture the general features of the measured spectra. This indicates the importance of accurately incorporating the dynamical aspect of electronic correlation among Fe 3d orbitals to reproduce the experimental excitation spectra. Specifically, the LDA+DMFT derived density of states exhibits a significant amount of Fe 3d states at the position of Bi lone pairs, implying that the latter are not alone in the spectral scenario. This fact might modify our interpretation about the origin of ferroelectric polarization in this material. Our study demonstrates that the combination of orbital cross sections for the constituent elements and broadening schemes for the spectral functions are crucial to explain the detailed structures of the experimental electronic spectra. Our magnetic excitation spectra computed from the LDA+DMFT result conform well with the inelastic neutron scattering data.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-351431 (URN)10.1103/PhysRevB.97.125120 (DOI)000427602000002 ()
Funder
Swedish Research CouncilCarl Tryggers foundation
Available from: 2018-06-01 Created: 2018-06-01 Last updated: 2018-06-01Bibliographically approved
Keshavarz, S., Kontos, S., Wardecki, D., Kvashnin, Y., Pereiro, M., Panda, S. K., . . . Svedlindh, P. (2018). Magnetic properties of Ruddlesden-Popper phases Sr3-&: A combined experimental and theoretical investigation. Physical Review Materials, 2(4), Article ID 044005.
Open this publication in new window or tab >>Magnetic properties of Ruddlesden-Popper phases Sr3-&: A combined experimental and theoretical investigation
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2018 (English)In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 4, article id 044005Article in journal (Refereed) Published
Abstract [en]

We present a comprehensive study of the magnetic properties of Sr3-xYx(Fe1.25Ni0.75)O-7(-delta )(0 <= x <= 0.75). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by a theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the Ned temperature (T-N) with an increase of Y concentrations and O occupancy. The NPD data reveal that all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the three-dimensional magnetic order is stabilized due to finite interlayer exchange couplings. The latter give rise to finite interlayer spin-spin correlations, which disappear above T-N.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-354116 (URN)10.1103/PhysRevMaterials.2.044005 (DOI)000430385300001 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-07-04Bibliographically approved
Schmitz-Antoniak, C., Schmitz, D., Warland, A., Darbandi, M., Haldar, S., Bhandary, S., . . . Wende, H. (2018). Suppression of the Verwey Transition by Charge Trapping. Annalen der Physik, 530(3), Article ID 1700363.
Open this publication in new window or tab >>Suppression of the Verwey Transition by Charge Trapping
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2018 (English)In: Annalen der Physik, ISSN 0003-3804, E-ISSN 1521-3889, Vol. 530, no 3, article id 1700363Article in journal (Refereed) Published
Abstract [en]

The Verwey transition in Fe3O4 nanoparticles with a mean diameter of 6.3 nm is suppressed after capping the particles with a 3.5 nm thick shell of SiO2. By X-ray absorption spectroscopy and its associated X-ray magnetic circular dichroism this suppression can be correlated to localized Fe2+ states and a reduced double exchange visible in different site-specific magnetization behavior in high magnetic fields. The results are discussed in terms of charge trapping at defects in the Fe3O4/ SiO2 interface and the consequent difficulties in the formation of the common phases of Fe3O4. By comparison to X-ray absorption spectra of bare Fe3O4 nanoparticles in course of the Verwey transition, particular changes in the spectral shape could be correlated to changes in the number of unoccupied d states for Fe ions at different lattice sites. These findings are supported by density functional theory calculations.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2018
Keywords
magnetite, nanoparticles, Verwey transition, X-ray absorption spectroscopy
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-354514 (URN)10.1002/andp.201700363 (DOI)000428350500010 ()
Funder
German Research Foundation (DFG), WE 2623/3-1
Available from: 2018-07-16 Created: 2018-07-16 Last updated: 2018-07-16Bibliographically 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.

Keywords
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.

Keywords
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
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ORCID iD: ORCID iD iconorcid.org/0000-0002-3687-4223

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