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Haldar, S., Bhandary, S., Vovusha, H. & Sanyal, B. (2018). Comparative study of electronic and magnetic properties of iron and cobalt phthalocyanine molecules physisorbed on two-dimensional MoS2 and graphene. Physical Review B, 98(8), Article ID 085440.
Open this publication in new window or tab >>Comparative study of electronic and magnetic properties of iron and cobalt phthalocyanine molecules physisorbed on two-dimensional MoS2 and graphene
2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 8, article id 085440Article in journal (Refereed) Published
Abstract [en]

In this paper, we have done a comparative theoretical study of electronic and magnetic properties of iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc) molecules physisorbed on a monolayer of MoS2 and graphene by density functional theory. Various types of physisorption sites have been considered for both surfaces. The lowest energy structure for both metal phthalocyanine (MPc) molecules physisorbed on MoS2 is a sulfur-top position, i.e., when the metal center of the molecule is on top of a sulfur atom. However, on graphene, the lowest energy structure for the FePc molecule is when a metal atom is on top of a bridge position. In contrast to this, the CoPc molecule prefers a carbon-top position. The adsorption of MPc molecules is stronger on the MoS(2 )surface than on graphene (similar to 2.5 eV higher physisorption energy). In these systems, spin dipole moments of the metal centers are antiparallel to the spin moments and hence a huge reduction of effective spin moment can be seen. The calculations of magnetic anisotropy energies using both variational and second-order perturbation approaches indicate no significant changes after physisorption. In case of the FePc and CoPc physisorption, respectively, an out-of-plane and an in-plane easy axis of magnetization can be observed. Our calculations indicate a reduction of MoS2 work function similar to 1 eV due to physisorption of MPc molecules while it does not change significantly in the case of graphene.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-364179 (URN)10.1103/PhysRevB.98.085440 (DOI)000443395600008 ()
Funder
Swedish Research Council, 2017-05447
Available from: 2018-11-01 Created: 2018-11-01 Last updated: 2018-11-01Bibliographically approved
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
La Torre, E., Smekhova, A., Schmitz-Antoniak, C., Ollefs, K., Eggert, B., Coester, B., . . . Wende, H. (2018). Local probe of irradiation-induced structural changes and orbital magnetism in Fe60Al40 thin films via an order-disorder phase transition. Physical Review B, 98(2), Article ID 024101.
Open this publication in new window or tab >>Local probe of irradiation-induced structural changes and orbital magnetism in Fe60Al40 thin films via an order-disorder phase transition
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 2, article id 024101Article in journal (Refereed) Published
Abstract [en]

Hard x-ray absorption and magnetic circular dichroism spectroscopy have been applied to study the consequential changes of the local environment around Fe atoms and their orbital polarizations in 40 nm thick Fe60Al40 thin films along the order-disorder (B2 -> A2) phase transition initiated by 20-keV Ne+ ion irradiation with fluences of (0.75-6) x 10(14) ions cm(-2). The analysis of the extended x-ray absorption fine structure spectra measured at the Fe K edge at room temperature revealed an increased number of Fe-Fe nearest neighbors from 3.47(7) to 5.0(1) and similar to 1% of volume expansion through the transition. The visualization of the Fe and Al nearest-neighbor rearrangement in the first coordination shell of Fe absorbers via the transition was carried out by wavelet transformations. The obtained changes in Fe coordination are evidently reflected in the x-ray magnetic circular dichroism spectra which show an increased orbital magnetic moment of Fe atoms and a pronounced magnetic multielectronic excitations peak at similar to 60 eV above the edge. The amplitudes of both peaks demonstrated similar dependencies on the irradiation fluence. The results of self-consistent density functional calculations on relaxed Fe60Al40 model structures for the ordered (B2) and the disordered (A2) phases are consistent with the experimental findings and point to the formation of Fe-rich regions in the films studied.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-361278 (URN)10.1103/PhysRevB.98.024101 (DOI)000437735700001 ()
Funder
Swedish Research Council
Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2018-09-27Bibliographically 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: 2018-08-24Bibliographically 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
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ORCID iD: ORCID iD iconorcid.org/0000-0002-3687-4223

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