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- 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. |
- Ntallis, Nikolaos, et al.
(författare)
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Macrospin model of an assembly of magnetically coupled core-shell nanoparticles
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:10
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Tidskriftsartikel (refereegranskat)abstract
- Highly sophisticated synthesis methods and experimental techniques allow for precise measurements of mag-netic properties of nanoparticles that can be reliably reproduced using theoretical models. Here, we investigate the magnetic properties of ferrite nanoparticles by using theoretical techniques based on Monte Carlo methods. We introduce three stages of sophistication in the macromagnetic model. First, by using tailor-made Hamil-tonians we study single nanoparticles. In a second stage, the internal structure of the nanoparticle is taken into consideration by defining an internal (core) and external (shell) region, respectively. In the last stage, an assembly of core-shell nanoparticles is considered. All internal magnetic couplings such as interatomic and intra-atomic exchange interactions or magnetocrystalline anisotropies have been estimated. Moreover, the hysteresis loops of the aforementioned three cases have been calculated and compared with recent experimental measurements. In the case of the assembly of nanoparticles, the hysteresis loops together with the zero-field-cooling and field-cooling curves are shown to be in a very good agreement with the experimental data. The current model provides an important tool to understand the internal structure of the nanoparticles together with the complex internal spin interactions of the core-shell ferrite nanoparticles.
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