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Attfield JP. Magnetism and the Trimeron Bond. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2022; 34:2877-2885. [PMID: 35814039 PMCID: PMC9261838 DOI: 10.1021/acs.chemmater.2c00275] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Revised: 03/14/2022] [Indexed: 05/06/2023]
Abstract
A review of progress in understanding the Verwey transition in magnetite (Fe3O4) over the past decade is presented. This electronic and structural transition at T V ≈ 125 K was reported in 1939 and has since been a contentious issue in magnetism. Long range Fe2+/Fe3+ charge ordering has been confirmed below the transition from crystal structure refinement, and Fe2+ orbital ordering and formation of trimerons through weak bonding of Fe2+ states to two Fe neighbors has been discovered. This model has accounted for many spectroscopic observations such as the 57Fe NMR frequencies. The trimeron lifetime has been measured, and trimeron soft modes have been observed. The origin of the first to second order crossover of Verwey transitions in doped magnetites has been revealed by a nanoparticle study. Electronic and structural fluctuations are found to persist to temperatures far above T V and local structural distortions track the bulk magnetization, disappearing at the 850 K Curie transition. New binary mixed-valent iron oxides discovered at high pressure are found to have electronic transitions and orbital molecule ground states similar to those of magnetite.
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Josten E, Angst M, Glavic A, Zakalek P, Rücker U, Seeck OH, Kovács A, Wetterskog E, Kentzinger E, Dunin-Borkowski RE, Bergström L, Brückel T. Strong size selectivity in the self-assembly of rounded nanocubes into 3D mesocrystals. NANOSCALE HORIZONS 2020; 5:1065-1072. [PMID: 32542274 DOI: 10.1039/d0nh00117a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The self-assembly of nanoparticles into highly ordered crystals is largely influenced by variations in the size and shape of the constituent particles, with crystallization generally not observed if their polydispersity is too large. Here, we report on size selectivity in the self-assembly of rounded cubic maghemite nanoparticles into three-dimensional mesocrystals. Different X-ray scattering techniques are used to study and compare a nanoparticle dispersion that is used later for self-assembly, an ensemble of mesocrystals grown on a substrate, as well as an individual mesocrystal. The individual μm-sized mesocrystal is isolated using a focused-ion-beam-based technique and investigated by the diffraction of a micro-focused X-ray beam. Structural analysis reveals that individual mesocrystals have a drastically smaller size dispersity of nanoparticles than that in the initial dispersion, implying very strong size selectivity during self-assembly. The small size dispersity of the nanoparticles within individual mesocrystals is accompanied by a very narrow lattice parameter distribution. In contrast, the lattice parameter distribution within all mesocrystals of an ensemble is about four times wider than that of individual mesocrystals, indicating significant size fractionalization between mesocrystals during self-assembly. The small size dispersity within each mesocrystal has important implications for their physical properties.
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Affiliation(s)
- Elisabeth Josten
- Jülich Centre for Neutron Science (JCNS) and Peter Grünberg Institute (PGI), JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.
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3
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Ovsyannikov SV, Bykov M, Bykova E, Kozlenko DP, Tsirlin AA, Karkin AE, Shchennikov VV, Kichanov SE, Gou H, Abakumov AM, Egoavil R, Verbeeck J, McCammon C, Dyadkin V, Chernyshov D, van Smaalen S, Dubrovinsky LS. Charge-ordering transition in iron oxide Fe4O5 involving competing dimer and trimer formation. Nat Chem 2016; 8:501-8. [PMID: 27102685 DOI: 10.1038/nchem.2478] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 02/15/2016] [Indexed: 11/09/2022]
Abstract
Phase transitions that occur in materials, driven, for instance, by changes in temperature or pressure, can dramatically change the materials' properties. Discovering new types of transitions and understanding their mechanisms is important not only from a fundamental perspective, but also for practical applications. Here we investigate a recently discovered Fe4O5 that adopts an orthorhombic CaFe3O5-type crystal structure that features linear chains of Fe ions. On cooling below ∼150 K, Fe4O5 undergoes an unusual charge-ordering transition that involves competing dimeric and trimeric ordering within the chains of Fe ions. This transition is concurrent with a significant increase in electrical resistivity. Magnetic-susceptibility measurements and neutron diffraction establish the formation of a collinear antiferromagnetic order above room temperature and a spin canting at 85 K that gives rise to spontaneous magnetization. We discuss possible mechanisms of this transition and compare it with the trimeronic charge ordering observed in magnetite below the Verwey transition temperature.
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Affiliation(s)
- Sergey V Ovsyannikov
- Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany
| | - Maxim Bykov
- Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany.,Laboratory of Crystallography, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany
| | - Elena Bykova
- Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany.,Laboratory of Crystallography, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany
| | | | - Alexander A Tsirlin
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia.,Experimental Physics VI, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, 86135 Augsburg, Germany
| | - Alexander E Karkin
- Institute of Metal Physics, Russian Academy of Sciences, Urals Division, GSP-170, 18 S. Kovalevskaya Str., Yekaterinburg 620041, Russia
| | - Vladimir V Shchennikov
- Institute of Metal Physics, Russian Academy of Sciences, Urals Division, GSP-170, 18 S. Kovalevskaya Str., Yekaterinburg 620041, Russia.,Institute for Solid State Chemistry, Russian Academy of Sciences, Urals Division, 91 Pervomayskaya Str., Yekaterinburg 620990, Russia
| | | | - Huiyang Gou
- Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany.,Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
| | - Artem M Abakumov
- Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.,Department of Chemistry, Moscow State University, Leninskie Gory 1-3, Moscow 119991, Russia
| | - Ricardo Egoavil
- Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Johan Verbeeck
- Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Catherine McCammon
- Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany
| | - Vadim Dyadkin
- Swiss-Norwegian Beamlines at the European Synchrotron Radiation Facility, 38000, Grenoble, France
| | - Dmitry Chernyshov
- Swiss-Norwegian Beamlines at the European Synchrotron Radiation Facility, 38000, Grenoble, France
| | - Sander van Smaalen
- Laboratory of Crystallography, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany
| | - Leonid S Dubrovinsky
- Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstrasse 30, D-95447, Bayreuth, Germany
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4
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Volkov S, Bubnova R, Bolotina N, Krzhizhanovskaya M, Belousova O, Filatov S. Incommensurate modulation and thermal expansion of Sr3B(2 + x)Si(1 - x)O(8 - x/2) solid solutions. ACTA CRYSTALLOGRAPHICA SECTION B, STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS 2015; 71:489-97. [PMID: 26428398 DOI: 10.1107/s2052520615011713] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 06/17/2015] [Indexed: 11/10/2022]
Abstract
Crystal structures of Sr3B(2 + x)Si(1 - x)O(8 - x/2) solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr3B2SiO8-Sr2B2O5 section of the SrO-B2O3-SiO2 system are refined using single-crystal X-ray diffraction data. Incommensurate structure modulations are mainly associated with various orientations of corner-sharing (B,Si)-polyhedra. Preference is given to the (3 + 2)-dimensional symmetry group Pnma(0βγ)000(0βγ)000 for a single crystal compared with an alternate model of a twin formed by monoclinic components, each of them corresponding to the (3 + 1)-dimensional symmetry group P2(1)/n(0βγ). Single-phase polycrystalline samples of solid solutions are investigated by high-temperature X-ray powder diffraction in air. Orientation preferences of the BO3 units lead to a strong anisotropy of thermal expansion. Negative expansion is observed along the a axis over the temperature range 303-753 K. Anisotropy decreases both on heating and decreasing of the boron content.
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Affiliation(s)
- Sergey Volkov
- Grebenshchikov Institute of Silicate Chemistry, Makarov Emb, St Petersburg 199053, Russian Federation
| | - Rimma Bubnova
- Grebenshchikov Institute of Silicate Chemistry, Makarov Emb, St Petersburg 199053, Russian Federation
| | - Nadezhda Bolotina
- Shubnikov Institute of Crystallography, Leninsky pr. 59, Moscow 119333, Russian Federation
| | - Maria Krzhizhanovskaya
- Department of Crystallography, St Petersburg State University, University Emb., 7/9, St Petersburg 199034, Russian Federation
| | - Olga Belousova
- Grebenshchikov Institute of Silicate Chemistry, Makarov Emb, St Petersburg 199053, Russian Federation
| | - Stanislav Filatov
- Department of Crystallography, St Petersburg State University, University Emb., 7/9, St Petersburg 199034, Russian Federation
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Eremin A, Kornek U, Stern S, Stannarius R, Araoka F, Takezoe H, Nádasi H, Weissflog W, Jákli A. Pattern-stabilized decorated polar liquid-crystal fibers. PHYSICAL REVIEW LETTERS 2012; 109:017801. [PMID: 23031131 DOI: 10.1103/physrevlett.109.017801] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Indexed: 06/01/2023]
Abstract
Geometric frustration gives rise to new fundamental phenomena and is known to yield the formation of exotic states of matter, such as incommensurate crystals, modulated liquid-crystalline phases, and phases stabilized by defects. In this Letter, we present a detailed study of polar structure of freely suspended fluid filaments in a polarization modulated liquid-crystal phase. We show that a periodic pattern of polarization-splay stripes separated by defect boundaries and decorating smectic layers can stabilize the structure of fluid fibers against the Rayleigh-Plateau instability. The instability is suppressed by the resistance of the defect structure to a radial compression of the cylindrical fibers. Our results provide direct experimental observation of a link between the stability of the liquid fibers, internal polar order, and geometrical constraints. They open a new perspective on a wide range of fluid polar fiber materials.
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Affiliation(s)
- Alexey Eremin
- Otto-von-Guericke Universität Magdeburg, Institute for Experimental Physics, ANP, 39016 Magdeburg, Germany.
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6
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de Groot J, Mueller T, Rosenberg RA, Keavney DJ, Islam Z, Kim JW, Angst M. Charge order in LuFe2O4: an unlikely route to ferroelectricity. PHYSICAL REVIEW LETTERS 2012; 108:187601. [PMID: 22681119 DOI: 10.1103/physrevlett.108.187601] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Indexed: 06/01/2023]
Abstract
We present the refinement of the crystal structure of charge-ordered LuFe2O4, based on single-crystal x-ray diffraction data. The arrangement of the different Fe-valence states, determined with bond-valence-sum analysis, corresponds to a stacking of charged Fe bilayers, in contrast with the polar bilayers previously suggested. This arrangement is supported by an analysis of x-ray magnetic circular dichroism spectra, which also evidences a strong charge-spin coupling. The nonpolar bilayers are inconsistent with charge order based ferroelectricity.
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Affiliation(s)
- J de Groot
- Peter Grünberg Institut PGI and Jülich Centre for Neutron Science JCNS, JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
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8
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Yang HX, Tian HF, Song YJ, Qin YB, Zhao YG, Ma C, Li JQ. Polar nanodomains and giant converse magnetoelectric effect in charge-ordered Fe2OBO3. PHYSICAL REVIEW LETTERS 2011; 106:016406. [PMID: 21231761 DOI: 10.1103/physrevlett.106.016406] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Indexed: 05/30/2023]
Abstract
The magnetoelectric coupling and polar nanodomains in the charge-ordered Fe2OBO3 have been extensively studied from room temperature down to 100 K. In situ TEM investigations demonstrate that the charge-ordering transition characterized by an incommensurate modulation could evidently result in remarkable polar nanodomains at low temperatures. This kind of nanodomain could play a critical role in triggering a high dielectric constant and notable dielectric dispersion as observed in Fe2OBO3. Moreover, measurements of the magnetoelectric coupling under electrical field demonstrate the existence of giant electrically induced changes in magnetization around the magnetic transition.
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Affiliation(s)
- H X Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
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Xu XS, Angst M, Brinzari TV, Hermann RP, Musfeldt JL, Christianson AD, Mandrus D, Sales BC, McGill S, Kim JW, Islam Z. Charge order, dynamics, and magnetostructural transition in multiferroic LuFe2O4. PHYSICAL REVIEW LETTERS 2008; 101:227602. [PMID: 19113523 DOI: 10.1103/physrevlett.101.227602] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2008] [Indexed: 05/27/2023]
Abstract
We investigated the series of temperature and field-driven transitions in LuFe2O4 by optical and Mössbauer spectroscopies, magnetization, and x-ray scattering in order to understand the interplay between charge, structure, and magnetism in this multiferroic material. We demonstrate that charge fluctuation has an onset well below the charge ordering transition, supporting the "order by fluctuation" mechanism for the development of charge order superstructure. Bragg splitting and large magneto-optical contrast suggest a low-temperature monoclinic distortion that can be driven by both temperature and magnetic field.
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Affiliation(s)
- X S Xu
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA
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10
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Angst M, Hermann RP, Christianson AD, Lumsden MD, Lee C, Whangbo MH, Kim JW, Ryan PJ, Nagler SE, Tian W, Jin R, Sales BC, Mandrus D. Charge order in LuFe2O4: antiferroelectric ground state and coupling to magnetism. PHYSICAL REVIEW LETTERS 2008; 101:227601. [PMID: 19113522 DOI: 10.1103/physrevlett.101.227601] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Indexed: 05/27/2023]
Abstract
X-ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to (1/3 1/3 3/2). The corresponding charge configuration, also found by electronic structure calculations as most stable, contains polar Fe/O double layers with antiferroelectric stacking. Diffuse scattering at 360 K, with (1/3 1/3 0) propagation, indicates ferroelectric short-range correlations between neighboring double layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled.
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Affiliation(s)
- M Angst
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
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