| 1. |
- Kons, Corisa, et al.
(författare)
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Influence of Hard/Soft Layer Ordering on Magnetization Reversal of Bimagnetic Nanoparticles : Implications for Biomedical/Theranostic Applications
- 2023
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 6:13, s. 10986-11000
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the spatial distribution of spin orientationinmagnetic nanoparticles consisting of hard and soft magnetic layers.The nanoparticles are synthesized in a core-shell sphericalmorphology where the target stoichiometry of the magnetically hard,high anisotropy layer is CoFe2O4 (CFO), whilethe synthesis protocol of the lower anisotropy material is known toproduce Fe3O4. The nanoparticles have a meandiameter of similar to 9.2-9.6 nm and are synthesized as two variants:a conventional hard/soft core-shell structure with a CFO core/FOshell (CFO@FO) and the inverted structure FO core/CFO shell (FO@CFO).High-resolution electron microscopy confirms the coherent spinel structureacross the core-shell boundary in both variants, while magnetometryindicates the nanoparticles are superparamagnetic at 300 K and developa considerable anisotropy at reduced temperatures. Low-temperature M vs H loops suggest a multistep reversal process. Smallangle neutron scattering (SANS) with full polarization analysis revealsa considerable alignment of the spins perpendicular to the field evenat fields approaching saturation. The perpendicular magnetizationis surprisingly correlated from one nanoparticle to the next, thoughthe interaction is of limited range. More significantly, the SANSdata reveal a pronounced difference in the reversal process of themagnetization parallel to the field for the two nanoparticle variants.For the CFO@FO nanoparticles, the core and shell magnetizations appearto track each other through the coercive region, while in the FO@CFOvariant, the softer Fe3O4 core reverses beforethe higher anisotropy CoFe2O4 shell, consistentwith expectations from mesoscale magnetic modeling. These resultshighlight the interplay between interfacial exchange coupling andanisotropy as a means to tune the composite properties of the nanoparticlesfor tailored applications including biomedical/theranostic uses.
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| 2. |
- Krycka, Kathryn L., et al.
(författare)
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Resolving Material-Specific Structures within Fe3O4 vertical bar gamma-Mn2O3 Core vertical bar Shell Nanoparticles Using Anomalous Small-Angle X-ray Scattering
- 2013
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 7:2, s. 921-931
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Tidskriftsartikel (refereegranskat)abstract
- Here it is demonstrated that multiple-energy, anomalous small-angle X-ray scattering (ASAXS) provides significant enhancement in sensitivity to internal material boundaries of layered nanoparticles compared with the traditional modeling of a single scattering energy, even for cases in which high scattering contrast naturally exists. Specifically, the material-specific structure of monodispersed Fe3O4 vertical bar gamma-Mn2O3 core vertical bar shell nanoparticles is determined, and the contribution of each component to the total scattering profile is identified with unprecedented clarity. We show that Fe3O4 vertical bar gamma-Mn2O3 core vertical bar shell nanoparticles with a diameter of 8.2 +/- 0.2 nm consist of a core with a composition near Fe3O4 surrounded by a (MnxFe1-x)(3)O-4 shell with a graded composition, ranging from x approximate to 0.40 at the Inner shell toward x approximate to 0.46 at the surface. Evaluation of the scattering contribution arising from the interference between material-specific layers additionally reveals the presence of Fe3O4 cores without a coating shell. Finally, it is found that the material-specific scattering profile shapes and chemical compositions extracted by this method are independent of the original input chemical compositions used in the analysis, revealing multiple-energy ASAXS as a powerful tool for determining internal nanostructured morphology even if the exact composition of the individual layers is not known a priori.
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| 3. |
- Saini, Apurve, et al.
(författare)
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Layering of magnetic nanoparticles at amorphous magnetic templates with perpendicular anisotropy
- 2020
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 16:33, s. 7676-7684
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Tidskriftsartikel (refereegranskat)abstract
- We reveal the assembly of magnetite nanoparticles of sizes 5 nm, 15 nm and 25 nm from dilute water-based ferrofluids onto an amorphous magnetic template with out-of-plane anisotropy. From neutron reflectometry experiments we extract density profiles and show that the particles self-assemble into layers at the magnetic surface. The layers are extremely stable against cleaning and rinsing of the substrate. The density of the layers is determined by and increases with the remanent magnetic moment of the particles.
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| 4. |
- Saini, Apurve, et al.
(författare)
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Magnetic particle self-assembly at functionalized interfaces
- 2021
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 37:14, s. 4064-4071
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Tidskriftsartikel (refereegranskat)abstract
- We study the assembly of magnetite nanoparticles in water-based ferrofluids in wetting layers close to silicon substrates with different functionalization without and with an out-of-plane magnetic field. For particles of nominal sizes 5, 15, and 25 nm, we extract density profiles from neutron reflectivity measurements. We show that self-assembly is only promoted by a magnetic field if a seed layer is formed at the silicon substrate. Such a layer can be formed by chemisorption of activated N-hydroxysuccinimide ester-coated nanoparticles at a (3-aminopropyl)triethoxysilane functionalized surface. Less dense packing is reported for physisorption of the same particles at a piranha-treated (strongly hydrophilic) silicon wafer, and no wetting layer is found for a self-assembled monolayer of octadecyltrichlorosilane (strongly hydrophobic) at the interface. We show that once the seed layer is formed and under an out-of-plane magnetic field further wetting layers assemble. These layers become denser with time, larger magnetic fields, higher particle concentrations, and larger moment of the nanoparticles.
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| 5. |
- Theis-Broehl, Katharina, et al.
(författare)
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Self assembly of magnetic nanoparticles at silicon surfaces
- 2015
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 11:23, s. 4695-4704
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Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectometry was used to study the assembly of magnetite nanoparticles in a water-based ferrofluid close to a silicon surface. Under three conditions, static, under shear and with a magnetic field, the depth profile is extracted. The particles have an average diameter of 11 nm and a volume density of 5% in a D2O-H2O mixture. They are surrounded by a 4 nm thick bilayer of carboxylic acid for steric repulsion. The reflectivity data were fitted to a model using a least square routine based on the Parratt formalism. From the scattering length density depth profiles the following behavior is concluded: the fits indicate that excess carboxylic acid covers the silicon surface and almost eliminates the water in the densely packed wetting layer that forms close to the silicon surface. Under constant shear the wetting layer persists but a depletion layer forms between the wetting layer and the moving ferrofluid. Once the flow is stopped, the wetting layer becomes more pronounced with dense packing and is accompanied by a looser packed second layer. In the case of an applied magnetic field the prolate particles experience a torque and align with their long axes along the silicon surface which leads to a higher particle density.
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| 6. |
- Theis-Broehl, Katharina, et al.
(författare)
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Self-assembly of Magnetic Nanoparticles in Ferrofluids on Different Templates by Neutron Reflectometry
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This article reviews the self-assembly of magnetite nanoparticles onto solid surfaces. We focus on neutron reflectometry studies providing information on the density and magnetization profiles of buried interfaces. Specific attention is given to the near-interface wetting layer and to examples of magnetite nanoparticles on a hydrophilic silicon crystal, one coated with (3-Aminopropyl)triethoxysilan, and finally one with a magnetic film with out-of-plane magnetization.
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| 7. |
- Theis-Broehl, Katharina, et al.
(författare)
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Self-Assembly of Magnetic Nanoparticles in Ferrofluids on Different Templates Investigated by Neutron Reflectometry
- 2020
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 10:6
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Forskningsöversikt (refereegranskat)abstract
- In this article we review the process by which magnetite nanoparticles self-assemble onto solid surfaces. The focus is on neutron reflectometry studies providing information on the density and magnetization depth profiles of buried interfaces. Specific attention is given to the near-interface "wetting" layer and to examples of magnetite nanoparticles on a hydrophilic silicon crystal, one coated with (3-Aminopropyl)triethoxysilane, and finally, one with a magnetic film with out-of-plane magnetization.
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| 8. |
- Theis-Bröhl, Katharina, et al.
(författare)
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Self-Assembled Layering of Magnetic Nanoparticles in a Ferrofluid on Silicon Surfaces
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 10:5, s. 5050-5060
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Tidskriftsartikel (refereegranskat)abstract
- This article describes the three-dimensional self assembly of monodisperse colloidal magnetite nanoparticles (NPs) from a dilute water-based ferrofluid onto a silicon surface and the dependence of the resultant magnetic structure on the applied field. The NPs assemble into close-packed layers on the surface followed by more loosely packed ones. The magnetic field-dependent magnetization of the individual NP layers depends on both the rotational freedom of the layer and the magnetization of the adjacent layers. For layers in which the NPs are more free to rotate, the easy axis of the NP can readily orient along the field direction. In more dense packing, free rotation of the NPs is hampered, and the NP ensembles likely build up quasi-domain states to minimize energy, which leads to lower magnetization in those layers. Detailed analysis of polarized neutron reflectometry data together with model calculations of the arrangement of the NPs within the layers and input from small-angle scattering measurements provide full characterization of the core/shell NP dimensions, degree of chaining, arrangement of the NPs within the different layers, and magnetization depth profile.
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