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| 2. |
- Feygenson, Mikhail, et al.
(författare)
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Probing spin waves in Co3O4 nanoparticles for magnonics applications
- 2024
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 16:3, s. 1291-1303
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of spinel nanoparticles can be controlled by synthesizing particles of a specific shape and size. The synthesized nanorods, nanodots and cubic nanoparticles have different crystal planes selectively exposed on the surface. The surface effects on the static magnetic properties are well documented, while their influence on spin waves dispersion is still being debated. Our ability to manipulate spin waves using surface and defect engineering in magnetic nanoparticles is the key to designing magnonic devices. We synthesized cubic and spherical nanoparticles of a classical antiferromagnetic material Co3O4 to study the shape and size effects on their static and dynamic magnetic proprieties. Using a combination of experimental methods, we probed the magnetic and crystal structures of our samples and directly measured spin wave dispersions using inelastic neutron scattering. We found a weak, but unquestionable, increase in exchange interactions for the cubic nanoparticles as compared to spherical nanoparticle and bulk powder reference samples. Interestingly, the exchange interactions in spherical nanoparticles have bulk-like properties, despite a ferromagnetic contribution from canted surface spins.
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| 3. |
- Lohstroh, Wiebke, et al.
(författare)
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Structural and optical properties of Mg2NiHx switchable mirrors upon hydrogen loading
- 2004
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 70, s. 165411-
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Tidskriftsartikel (refereegranskat)abstract
- The structural, thermodynamic and optical properties of Mg2Ni thin films covered with Pd are investigatedupon exposure to hydrogen. Similar to bulk, thin films of metallic Mg2Ni take up 4 hydrogen per formula unitand semiconducting transparent Mg2NiH4−d is formed. The dielectric function e˜ of Mg2Ni and fully loadedMg2NiH4−d is determined from reflection and transmission measurements using a Drude-Lorentz parametrization.Besides the two “normal” optical states of a switchable mirror—metallic reflecting and semiconductingtransparent—Mg2NiHx exhibit a third “black” state at intermediate hydrogen concentrations with low reflectionand essentially zero transmission. This state originates from a subtle interplay of the optical properties of theconstituent materials and a self-organized double layering of the film during loading. Mg2NiH4−d preferentiallynucleates at the film/substrate interface and not—as intuitively expected—close to the catalytic Pd cappinglayer. Using e˜Mg2Ni and e˜Mg2NiH4and this loading sequence, the optical response at all hydrogen concentrationscan be described quantitatively. The uncommon hydrogen loading sequence is confirmed by x-ray diffractionand hydrogen profiling using the resonant nuclear reaction 1Hs15N,agd12C. Pressure-composition isothermssuggest that
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| 4. |
- Pistidda, Claudio, et al.
(författare)
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Pressure Effect on the 2NaH+MgB2 Hydrogen Absorption Reaction
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:49, s. 21816-21823
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen absorption mechanism of the 2NaH + MgB2 system has been investigated in detail. Depending on the applied hydrogen pressure, different intermediate phases are observed. In the case of absorption measurements performed under 50 bar of hydrogen pressure, NaBH4 is found not to be formed directly. Instead, first an unknown phase is formed, followed upon further heating by the formation of NaMgH3 and a NaH-NaBH4 molten salt mixture; only at the end after heating to 380 degrees C do the reflections of the crystalline NaBH4 appear. In contrast, measurements performed at lower hydrogen pressure (5 bar of H-2), but under the same temperature conditions, demonstrate that the synthesis of NaBH4 is possible without occurrence of the unknown phase and of NaMgH3. This indicates that the reaction path can be tuned by the applied hydrogen pressure. The formation of a NaH-NaBH4 molten salt mixture is observed also for the measurement performed under 5 bar of hydrogen pressure with the formation of free Mg. However, under this pressure condition the formation of crystalline NaBH4 is observed only during cooling at 367 degrees C. For none of the applied experimental conditions has it been possible to achieve the theoretical gravimetric hydrogen capacity of 7.8 wt %.
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| 5. |
- Pistidda, Claudio, et al.
(författare)
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Synthesis of amorphous Mg(BH4)(2) from MgB2 and H-2 at room temperature
- 2010
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 508:1, s. 212-215
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Tidskriftsartikel (refereegranskat)abstract
- Due to its high hydrogen content and its favourable overall thermodynamics magnesium tetrahydroborate has been considered interesting for hydrogen storage applications. In this work we show that unsolvated amorphous magnesium tetrahydroborate can be obtained by reactive ball milling of commercial MgB2 under 100 bar hydrogen atmosphere. The material was characterized by solid-state NMR which showed the characteristic features of Mg(BH4)(2), together with those of higher borohydride species. High pressure DSC and TPD-MS showed thermal behaviour similar to that of Mg(BH4)(2) but with broadened signals. In situ synchrotron X-ray powder diffraction confirmed the amorphous state of the material and showed the typical crystalline decomposition products of Mg(BH4)(2) at elevated temperatures. (C) 2010 Elsevier B.V. All rights reserved.
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