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Brumboiu, I. E., Eriksson, O. & Norman, P. (2019). Atomic photoionization cross sections beyond the electric dipole approximation. Journal of Chemical Physics, 150(4), Article ID 044306.
Open this publication in new window or tab >>Atomic photoionization cross sections beyond the electric dipole approximation
2019 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 4, article id 044306Article in journal (Refereed) Published
Abstract [en]

A methodology is developed to compute photoionization cross sections beyond the electric dipole approximation from response theory, using Gaussian type orbitals and plane waves for the initial and final states, respectively. The methodology is applied to compute photoionization cross sections of atoms and ions from the first four rows of the periodic table. Analyzing the error due to the plane wave description of the photoelectron, we find kinetic energy and concomitant photon energy thresholds above which the plane wave approximation becomes applicable. The correction introduced by going beyond the electric dipole approximation increases with photon energy and depends on the spatial extension of the initial state. In general, the corrections are below 10% for most elements, at a photon energy reaching up to 12 keV.

National Category
Atom and Molecular Physics and Optics Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-377346 (URN)10.1063/1.5083649 (DOI)000457414600056 ()30709292 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020Swedish Research Council, 621-2014-4646eSSENCE - An eScience Collaboration
Available from: 2019-02-25 Created: 2019-02-25 Last updated: 2019-02-25Bibliographically approved
Ivanov, S., Beran, P., Bush, A. A., Sarkar, T., Shafeie, S., Wang, D., . . . Mathieu, R. (2019). Cation ordering, ferrimagnetism and ferroelectric relaxor behavior in Pb(Fe1-xScx)(2/3)W1/3O3 solid solutions. European Physical Journal B: Condensed Matter Physics, 92(8), Article ID 163.
Open this publication in new window or tab >>Cation ordering, ferrimagnetism and ferroelectric relaxor behavior in Pb(Fe1-xScx)(2/3)W1/3O3 solid solutions
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2019 (English)In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 92, no 8, article id 163Article in journal (Refereed) Published
Abstract [en]

Ceramic samples of the multiferroic perovskite Pb(Fe1-xScx)(2/3)W1/3O3 with 0 <= x <= 0.4 have been synthesized using a conventional solid-state reaction method, and investigated experimentally and theoretically using first-principle calculations. Rietveld analyses of joint synchrotron X-ray and neutron diffraction patterns show the formation of a pure crystalline phase with cubic (Fm3(_)m) structure with partial ordering in the B-sites. The replacement of Fe by Sc leads to the increase of the cation order between the B and B '' sites. As the non-magnetic Sc3+ ions replace the magnetic Fe3+ cations, the antiferromagnetic state of PbFe2/3W1/3O3 is turned into a ferrimagnetic state reflecting the different magnitude of the magnetic moments on the B ' and B '' sites. The materials remain ferroelectric relaxors with increasing Sc content. Results from experiments on annealed and quenched samples show that the cooling rate after high temperature annealing controls the degree of cationic order in Pb(Fe1-xScx)(2/3)W1/3O3 and possibly also in the undoped PbFe2/3W1/3O3.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Solid State and Materials
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-392576 (URN)10.1140/epjb/e2019-100149-9 (DOI)000477626500002 ()
Funder
Swedish Research Council
Available from: 2019-09-09 Created: 2019-09-09 Last updated: 2019-09-09Bibliographically approved
Jana, S., Panda, S. K., Phuyal, D., Pal, B., Mukherjee, S., Dutta, A., . . . Sarma, D. D. (2019). Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO3. Physical Review B, 99(7), Article ID 075106.
Open this publication in new window or tab >>Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO3
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075106Article in journal (Refereed) Published
Abstract [en]

We explore the effects of electron doping in lanthanum ferrite, LaFeO3 by doping Mo at the Fe sites. Based on magnetic, transport, scanning tunneling spectroscopy, and x-ray photoelectron spectroscopy measurements, we find that the large gap, charge-transfer, antiferromagnetic (AFM) insulator LaFeO3 becomes a small gap AFM band insulator at low Mo doping. With increasing doping concentration, Mo states, which appear around the Fermi level, is broadened and become gapless at a critical doping of 20%. Using a combination of calculations based on density functional theory plus Hubbard U (DFT+U) and x-ray absorption spectroscopy measurements, we find that the system shows charge disproportionation (CD) in Fe ions at 25% Mo doping, where two distinct Fe sites, having Fe2+ and Fe3+ nominal charge states appear. A local breathing-type lattice distortion induces the charge disproportionation at the Fe site without destroying the antiferromagnetic order. Our combined experimental and theoretical investigations establish that the Fe states form a CD antiferromagnet at 25% Mo doping, which remains insulating, while the appearance of Mo states around the Fermi level is showing an indication towards the insulator-metal transition.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-378537 (URN)10.1103/PhysRevB.99.075106 (DOI)000458168300001 ()
Funder
Swedish Research Council, 2016-4524Knut and Alice Wallenberg Foundation, 2012.0031Swedish Energy Agency, P43294-1EU, European Research Council, CorrelMat-617196Swedish Research Council, 2016-03278Swedish Research CouncilSwedish Foundation for Strategic Research Carl Tryggers foundation , CTS-17:376eSSENCE - An eScience CollaborationStandUp
Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-03-21Bibliographically approved
Nieves, P., Arapan, S., Maudes-Raedo, J., Marticorena-Sanchez, R., Del Brio, N. L., Kovacs, A., . . . Cuesta-Lopez, S. (2019). Database of novel magnetic materials for high-performance permanent magnet development. Computational materials science, 168, 188-202
Open this publication in new window or tab >>Database of novel magnetic materials for high-performance permanent magnet development
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2019 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 168, p. 188-202Article in journal (Refereed) Published
Abstract [en]

This paper describes the open Novamag database that has been developed for the design of novel Rare-Earth free/lean permanent magnets. Its main features as software technologies, friendly graphical user interface, advanced search mode, plotting tool and available data are explained in detail. Following the philosophy and standards of Materials Genome Initiative, it contains significant results of novel magnetic phases with high magnetocrystalline anisotropy obtained by three computational high-throughput screening approaches based on a crystal structure prediction method using an Adaptive Genetic Algorithm, tetragonally distortion of cubic phases and tuning known phases by doping. Additionally, it also includes theoretical and experimental data about fundamental magnetic material properties such as magnetic moments, magnetocrystalline anisotropy energy, exchange parameters, Curie temperature, domain wall width, exchange stiffness, coercivity and maximum energy product, that can be used in the study and design of new promising high-performance Rare-Earth free/lean permanent magnets. The results therein contained might provide some insights into the ongoing debate about the theoretical performance limits beyond Rare-Earth based magnets. Finally, some general strategies are discussed to design possible experimental routes for exploring most promising theoretical novel materials found in the database.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Database, Magnetic materials, Permanent magnets, Materials Genome Initiative, High-throughput, VASP, Computer simulation, Novamag
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-390369 (URN)10.1016/j.commatsci.2019.06.007 (DOI)000475556000024 ()
Funder
EU, Horizon 2020, 686056Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research Swedish Energy AgencyStandUpeSSENCE - An eScience Collaboration
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-12Bibliographically approved
Tian, L.-Y., Levamaki, H., Eriksson, O., Kokko, K., Nagy, A., Delczeg-Czirjak, E. K. & Vitos, L. (2019). Density Functional Theory description of the order-disorder transformation in Fe-Ni. Scientific Reports, 9, Article ID 8172.
Open this publication in new window or tab >>Density Functional Theory description of the order-disorder transformation in Fe-Ni
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8172Article in journal (Refereed) Published
Abstract [en]

The thermodynamic ordering transformation of tetragonal FeNi system is investigated by the Exact Muffin-Tin Orbitals (EMTO) method. The tetragonal distortion of the unit cell is taken into account and the free energy is calculated as a function of long-range order and includes the configurational, vibrational, electronic and magnetic contributions. We find that both configurational and vibrational effects are important and that the vibrational effect lowers the predicted transformation temperature by about 480 K compared to the value obtained merely from the configurational free energy. The predicted temperature is in excellent agreement with the experimental value when all contributions are taken into account. We also perform spin dynamics calculations for the magnetic transition temperature and find it to be in agreement with the experiments. The present research opens new opportunities for quantum-mechanical engineering of the chemical and magnetic ordering in tetrataenite.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-387732 (URN)10.1038/s41598-019-44506-7 (DOI)000469912700013 ()31160612 (PubMedID)
Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-06-25Bibliographically approved
Huttmann, F., Rothenbach, N., Kraus, S., Ollefs, K., Arruda, L. M., Bernien, M., . . . Wende, H. (2019). Europium Cyclooctatetraene Nanowire Carpets: A Low-Dimensional, Organometallic, and Ferromagnetic Insulator. Journal of Physical Chemistry Letters, 10(5), 911-917
Open this publication in new window or tab >>Europium Cyclooctatetraene Nanowire Carpets: A Low-Dimensional, Organometallic, and Ferromagnetic Insulator
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2019 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 5, p. 911-917Article in journal (Refereed) Published
Abstract [en]

We investigate the magnetic and electronic properties of europium cyclooctatetraene (EuCot) nanowires by means of low-temperature X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM) and spectroscopy (STS). The EuCot nanowires are prepared in situ on a graphene surface. STS measurements identify EuCot as an insulator with a minority band gap of 2.3 eV. By means of Eu M-5,M-4 edge XMCD, orbital and spin magnetic moments of (-0.1 +/- 0.3)mu(B) and (+7.0 +/- 0.6)mu(B), respectively, were determined. Field-dependent measurements of the XMCD signal at the Eu M-5 edge show hysteresis for grazing X-ray incidence at 5 K, thus confirming EuCot as a ferromagnetic material. Our density functional theory calculations reproduce the experimentally observed minority band gap. Modeling the experimental results theoretically, we find that the effective interatomic exchange interaction between Eu atoms is on the order of millielectronvolts, that magnetocrystalline anisotropy energy is roughly half as big, and that dipolar energy is approximately ten times lower.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-380459 (URN)10.1021/acs.jpclett.8b03711 (DOI)000461271700003 ()30717591 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2013.0020Knut and Alice Wallenberg Foundation, 2012.0031Swedish Foundation for Strategic Research
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-03-28Bibliographically approved
Hellsvik, J., Thonig, D., Modin, K., Iusan, D., Bergman, A., Eriksson, O., . . . Delin, A. (2019). General method for atomistic spin-lattice dynamics with first-principles accuracy. Physical Review B, 99(10), Article ID 104302.
Open this publication in new window or tab >>General method for atomistic spin-lattice dynamics with first-principles accuracy
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104302Article in journal (Refereed) Published
Abstract [en]

We present a computationally efficient and general first-principles based method for spin-lattice simulations for solids and clusters. The method is based on a coupling of atomistic spin dynamics and molecular dynamics simulations, expressed through a spin-lattice Hamiltonian, where the bilinear magnetic term is expanded up to second order in displacement. The effect of first-order spin-lattice coupling on the magnon and phonon dispersion in bcc Fe is reported as an example, and we observe good agreement with previous simulations. We also illustrate the coupled spin-lattice dynamics method on a more conceptual level, by exploring dissipation-free spin and lattice motion of small magnetic clusters (a dimer, trimer, and tetramer). The method discussed here opens the door for a quantitative description and understanding of the microscopic origin of many fundamental phenomena of contemporary interest, such as ultrafast demagnetization, magnetocalorics, and spincaloritronics.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-381080 (URN)10.1103/PhysRevB.99.104302 (DOI)000461953800003 ()
Funder
Swedish Research CouncilSwedish Energy AgencySwedish Foundation for Strategic Research Swedish Research Council, 2016-06955Knut and Alice Wallenberg Foundation
Available from: 2019-04-23 Created: 2019-04-23 Last updated: 2019-04-23Bibliographically approved
Arapan, S., Nieves, P., Cuesta-Lopez, S., Gusenbauer, M., Oezelt, H., Schrefl, T., . . . Eriksson, O. (2019). Influence of antiphase boundary of the MnAl tau-phase on the energy product. PHYSICAL REVIEW MATERIALS, 3(6), Article ID 064412.
Open this publication in new window or tab >>Influence of antiphase boundary of the MnAl tau-phase on the energy product
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2019 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, no 6, article id 064412Article in journal (Refereed) Published
Abstract [en]

In this paper, we use a multiscale approach to describe a realistic model of a permanent magnet based on MnAl tau-phase and elucidate how the antiphase boundary defects present in this material affect the energy product. We show how the extrinsic properties of a microstructure depend on the intrinsic properties of a structure with defects by performing micromagnetic simulations. For an accurate estimation of the energy product of a realistic permanent magnet based on the MnAl tau-phase with antiphase boundaries, we quantify exchange interaction strength across the antiphase boundary defect with a simple approach derived from first-principles calculations. These two types of calculations, performed at different scales, are linked via atomistic spin-dynamics simulations.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Metallurgy and Metallic Materials Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-390677 (URN)10.1103/PhysRevMaterials.3.064412 (DOI)000473314400003 ()
Funder
EU, Horizon 2020, 686056Swedish Research CouncilSwedish Foundation for Strategic Research , EM6-0039Swedish Energy Agency
Available from: 2019-08-15 Created: 2019-08-15 Last updated: 2019-08-15Bibliographically approved
Schönhöbel, A. M., Madugundo, R., Vekilova, O. Y., Eriksson, O., Herper, H. C., Barandiaran, J. M. & Hadjipanayis, G. C. (2019). Intrinsic magnetic properties of SmFe12-xVx alloys with reduced V-concentration. Journal of Alloys and Compounds, 786, 969-974
Open this publication in new window or tab >>Intrinsic magnetic properties of SmFe12-xVx alloys with reduced V-concentration
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2019 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 786, p. 969-974Article in journal (Refereed) Published
Abstract [en]

In this work, we present experimental and theoretical results on SmFe12-xVx (x = 0.5 - 2.0) alloys with the ThMn12 (1:12) structure as possible candidates for rare earth-lean permanent magnets. The compound with x = 2 has been previously reported to have a Curie temperature of 330 degrees C, saturation magnetization of about 80 Am-2/kg, and anisotropy field around 9 T. We have synthesized the SmFe11V compound with a nearly pure 1:12 phase; the x = 0.5 compound couldn't be synthesized. The relative stability of the x = 1, 2 compounds was addressed theoretically by enthalpy calculations from first principles. The newly synthesized SmFe11V compound has a Curie temperature of 361 degrees C and saturation magnetization of 115 Am-2/kg (1.12 T). The anisotropy field has been obtained in magnetically-oriented fine powders, and is around 11 T. These parameters make SmFe11V a good candidate for a new kind of high energy, rare earth-lean permanent magnets. 

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Rare-earth lean permanent magnets, ThMn12-type structure, Iron alloys, Magnetocrystalline anisotropy, Ab initio calculations, Density functional theory
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-381104 (URN)10.1016/j.jallcom.2019.01.332 (DOI)000461778600114 ()
Funder
EU, Horizon 2020, 686056EU, Horizon 2020, 691235Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research StandUpeSSENCE - An eScience CollaborationSwedish Foundation for Strategic Research
Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-04-04Bibliographically approved
Brumboiu, I. E., Haldar, S., Lüder, J., Eriksson, O., Herper, H. C., Brena, B. & Sanyal, B. (2019). Ligand effects on the linear response Hubbard U: The case of transition metal phthalocyanines. Journal of Physical Chemistry A, 123(14), 3214-3222
Open this publication in new window or tab >>Ligand effects on the linear response Hubbard U: The case of transition metal phthalocyanines
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2019 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 123, no 14, p. 3214-3222Article in journal (Refereed) Published
Abstract [en]

It is established that density functional theory (DFT) + U is a better choice compared to DFT for describing the correlated electron metal center in organometallics. The value of the Hubbard U parameter may be determined from linear response, either by considering the response of the metal site alone or by additionally considering the response of other sites in the compound. We analyze here in detail the influence of ligand shells of increasing size on the U parameter calculated from the linear response for five transition metal phthalocyanines. We show that the calculated multiple-site U is larger than the single-site U by as much as 1 eV and the ligand atoms that are mainly responsible for this difference are the isoindole nitrogen atoms directly bonded to the central metal atom. This suggests that a different U value may be required for computations of chemisorbed molecules compared to physisorbed and gas-phase cases.

National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-300117 (URN)10.1021/acs.jpca.8b11940 (DOI)000464768100011 ()30892039 (PubMedID)
Funder
Swedish Research Council, 2014-3776Swedish Research Council, 2016-05366Swedish Research Council, 2017-05447Knut and Alice Wallenberg Foundation, KAW-2013.0020Swedish National Infrastructure for Computing (SNIC)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2019-05-15Bibliographically approved
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