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- Ahniyaz, Anwar, et al.
(författare)
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Preparation of iron oxide nanocrystals by surfactant-free or oleic acid-assisted thermal decomposition of a Fe(III) alkoxide
- 2008
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 320:6, s. 781-787
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Tidskriftsartikel (refereegranskat)abstract
- A new non-hydrolytic, alkoxide-based route was developed to synthesize iron oxide nanocrystals. Surfactant-free thermal decomposition of the iron 2-methoxy-ethoxide precursors results in the formation of uniform iron oxide nanocrystals with an average size of 5.6 nm. Transmission electron microscope study shows that the nanocrystals are protected against aggregation by a repulsive surface layer, probably originating from the alkoxy-alkoxide ligands. Addition of oleic acid resulted in monodisperse nanocrystals with an average size of 4 nm. Mössbauer analysis confirmed that the nanocrystals mainly consisted of maghemite. Analysis of the magnetic hysteresis loop measurements and the zero field and field cooled measurements displayed an excellent fit to established theories for single-domain superparamagnetic nanocrystals and the size of the magnetic domains correlated well to the crystallite size obtained from transmission electron microscope.
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| 5. |
- Disch, Sabrina, et al.
(författare)
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Shape Induced Symmetry in Self-Assembled Mesocrystals of Iron Oxide Nanocubes
- 2011
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 11:4, s. 1651-1656
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Tidskriftsartikel (refereegranskat)abstract
- Grazing incidence small-angle scattering and electron microscopy have been used to show for the first time that nonspherical nanoparticles can assemble into highly ordered body-centered tetragonal mesocrystals. Energy models accounting for the directionality and magnitude of the van der Waals and dipolar interactions as a function of the degree of truncation of the nanocubes illustrated the importance of the directional dipolar forces for the formation of the initial nanocube clusters and the dominance of the van der Waals multibody interactions in the dense packed arrays.
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- Gamage, Eranga H., et al.
(författare)
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As-Se Pentagonal Linkers to Induce Chirality and Polarity in Mixed-Valent Fe-Se Tetrahedral Chains Resulting in Hidden Magnetic Ordering
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:25, s. 11283-11295
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Tidskriftsartikel (refereegranskat)abstract
- A novel mixed-valent hybrid chiral and polar compound, Fe7As3Se12(en)(6)(H2O), has been synthesized by a single-step solvothermal method. The crystal structure consists of 1D [Fe5Se9] chains connected via [As3Se2]-Se pentagonal linkers and charge-balancing interstitial [Fe(en)(3)](2+) complexes (en = ethylenediamine). Neutron powder diffraction verified that interstitial water molecules participate in the crystal packing. Magnetic polarizability of the produced compound was confirmed by X-ray magnetic circular dichroism (XMCD) spectroscopy. X-ray absorption spectroscopy (XAS) and Fe-57 Mossbauer spectroscopy showed the presence of mixed-valent Fe2+/Fe3+ in the Fe-Se chains. Magnetic susceptibility measurements reveal strong antiferromagnetic nearest neighbor interactions within the chains with no apparent magnetic ordering down to 2 K. Hidden short-range magnetic ordering below 70 K was found by Fe-57 Mossbauer spectroscopy, showing that a fraction of the Fe3+/Fe2+ in the chains are magnetically ordered. Nevertheless, complete magnetic ordering is not achieved even at 6 K. Analysis of XAS spectra demonstrates that the fraction of Fe3+ in the chain increases with decreasing temperature. Computational analysis points out several competing ferrimagnetic ordered models within a single chain. This competition, together with variation in the Fe oxidation state and additional weak intrachain interactions, is hypothesized to prevent long-range magnetic ordering.
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- Häggström, Lennart, et al.
(författare)
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Mossbauer study of a ball-milled Co0.40Fe0.10Zr0.10B0.40 alloy
- 2022
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 560
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Fe-57 Mossbauer spectroscopy has been used to identify various Fe-restricted components formed in a ball-milled Co0.40Fe0.10Zr0.10B0.40 alloy for different milling times of 0 h, 8 h, 24 h, 72 h, 120 h, and 190 h. It is shown that the initial ball-milling results in formation of amorphous Fe1-xCox alloys. Further ball-milling introduces B into the neighborhood of the Fe atoms, and amorphous components with 3 and 4 B atoms as nearest-neighbors and next-nearest-neighbors are observed. Although the investigation about alloying of Fe and Zr is more difficult, it is concluded that there is no evidence of any crystalline FeZr phase. Furthermore, annealing the 190 h milled sample shows that crystalline Fe1-xCox alloys with very low x-values (x < 0.02) are formed.
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- Häggström, Lennart, et al.
(författare)
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Mössbauer and magnetisation studies of iron oxide nanocrystals
- 2008
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 183:1-3, s. 49-53
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Tidskriftsartikel (refereegranskat)abstract
- Monodisperse iron oxide nanocrystals have been produced following non-hydrolytic, thermal decomposition routes. Spherically shaped particles with diameter of 4 and 12 nm and cubic shaped particles with an edge length of 9 nm have been studied. The particles have been shown to consist of mainly maghemite. A reduction of the saturation magnetic hyperfine field is observed for the 4 nm particles as compared to the corresponding bulk value. The anisotropy energy determined from the temperature variation of the magnetic hyperfine field was strongly enhanced for the 4 nm particles.
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| 9. |
- Häggström, Lennart, et al.
(författare)
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Thickness dependent crystallographic transition in Fe/Ni multilayers
- 2010
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 217, s. 012112-
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Tidskriftsartikel (refereegranskat)abstract
- The crystallog. transition between bcc- and fcc-structures has been studied in Fe/Ni multilayers with Moessbauer spectroscopy and X-ray diffraction. Layered structures have been confirmed and the structures depends both on individual layer thickness and the ratio of the constituents. Two sets of samples are made: the Fe layer thickness kept const. to 12 monolayer (ML) and 24ML, while the Ni layer thicknesses varied from 3 to 12ML. When the Ni layer is thin, the Fe/Ni multilayers have the bcc phase. When the thickness of Ni layer reaches 6ML and larger, a gradual transition to the fcc phase occurs. Moessbauer spectroscopy studies confirm the existence of a magnetic Fe bcc phase with in-plane magnetization in all samples, two magnetic fcc phases with fields of 28 T and 10 T and small amts. of nonmagnetic fcc phases in the thicker films. The obsd. behavior can be attributed to the existence of two types of interfaces which are not necessary overlapping each other: An elemental interface between Fe and Ni and a structural interface between fcc and bcc phases. [on SciFinder(R)]
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| 10. |
- Kamali-Moghaddam, Saeed, 1967-
(författare)
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3d Transition Metals Studied by Mössbauer Spectroscopy
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Layered crystals with magnetic elements as Co and Fe have been studied. In TlCo2Se2, where Co atoms in one sheet are separated by Tl and Se from the next Co sheet, magnetic interaction within and between the sheets have been studied. Samples doped with 4% 57Fe replaced Co, show a magnetic spiral character with hyperfine fields in a flower shape in the ab-plane. The magnetic moment of 0.46 μB per Co atom derived from the average field is in good agreement with the result from neutron diffraction. In TlCu1.73Fe0.27Se2 the easy axis of magnetisation is the c-axis. The magnetic moment calculated from the Mössbauer data and SQUID magnetrometry is 0.97 μB per Fe atom with TC = 55(5) K. Multilayers of different elements have been studied. The effect of vanadium atoms on iron atoms at the interface of FeNi/V multilayers has been determined and the intermixing at the interface has been calculated to be 2-3 monolayers. For FeNi/Co 1/1 monolayer the magnetic hyperfine field (Bhf) is 45° out-of-plane, while for superlattices containing 2 to 5 monolayers it is in the plane. An study on Fe/Co superlattice were done by experimental, theoretical and simulational methods. The Bhf is highest for the Fe at the second layer next to the interface and gets the bulk value in the centre of thicker Fe layers. Studied magnetic nanoparticles coated with a lipid bilayer (magnetoliposomes) are found to have the magnetite structure but being non-stoichiometric as a result of the manufacturing process. The composition was approximately 32% γ-Fe2O3 and 68% Fe3O4. The oxidation evolution and its effect on magnetic properties of Fe clusters were also studied by means of different techniques. The extraction and insertion mechanism of lithium in the cathode material Li2FeSiO4 has been monitored by in situ x-ray diffraction and Mössbauer spectroscopy during the first two cycles. The relative amount of Fe+3/ Fe+2 at each end state was in good agreement with the results obtained from electrochemical measurements. A possible explanation to the observed lowering of the potential plateau from 3.10 to 2.80 V occurring during the first cycle, involves a structural rearrangement process in which some of the Li ions and the Fe ions are interchanged. The behaviour of small amounts of Fe in brass is investigated using Mössbauer spectroscopy. It was shown that a heat treatment can increase the amount of the precipitates of γ-Fe and ~650° C is the optimal treatment for having the highest amount of this phase.
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