| 1. |
- Margaris, G., et al.
(författare)
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Superspin glass state in a diluted nanoparticle system stabilized by interparticle interactions mediated by an antiferromagnetic matrix
- 2017
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Ingår i: Nanotechnology. - : IOP PUBLISHING LTD. - 0957-4484 .- 1361-6528. ; 28:3
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Tidskriftsartikel (refereegranskat)abstract
- In nanoparticle systems consisting of two magnetic materials (bi-magnetic nanoparticles or nanoparticles embedded in a magnetic matrix), there is a constantly growing interest in the investigation of the interplay between interparticle interactions and the nanoparticle-matrix interface exchange coupling, because of its enormous impact on a number of technological applications. The understanding of the mechanisms of such interplay is a great challenge, as it would allow controlling equilibrium and non-equilibrium magnetization dynamics of exchange coupled nanoparticles systems and finely tuning their anisotropy. Here, we provide evidence that this interplay leads to a collective superspin glass (SSG) behavior in a system of diluted ferromagnetic. (FM) nanoparticles embedded in an antiferromagnetic (AFM) matrix (5% volume fraction of Co particles in Mn film matrix). We have developed a novel mesoscopic model to study the influence of interparticle interaction on the exchange bias (EB) and the dynamical behavior of assemblies of FM nanoparticles embedded in a granular AFM matrix. Our mesoscopic model is based on reducing the amount of simulated spins to the minimum number necessary to describe the magnetic structure of the system and introducing the adequate exchange parameters between the different spins. The model replicates remarkably well the observed static and dynamical SSG properties as well as the EB behavior. In addition, the proposed model well explains the role of the significant Co/Mn alloying and of the granularity of the matrix in mediating interparticle interactions through exchange and dipole-dipole coupling between the uncompensated moments of its grains and the exchange interaction at the Co/Mn interface.
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| 2. |
- Muscas, Giuseppe, et al.
(författare)
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Magnetic Properties of Small Magnetite Nanocrystals
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 117:44, s. 23378-23384
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Tidskriftsartikel (refereegranskat)
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| 3. |
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| 4. |
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| 5. |
- Peddis, D., et al.
(författare)
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Magnetic anisotropy and magnetization dynamics of Fe nanoparticles embedded in Cr and Ag matrices
- 2015
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Ingår i: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; 95:33, s. 3798-3807
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Tidskriftsartikel (refereegranskat)abstract
- Static and dynamical magnetic properties of Fe nanoparticles (NPs) embedded in non-magnetic (Ag) and antiferromagnetic (Cr) matrices with a volume filling fraction (VFF) of 10% have been investigated. In both Fe@Ag and Fe@Cr nanocomposites, the Fe NPs have a narrow size distribution, with a mean particle diameter around 2nm. In both samples, the saturation magnetization reaches that of Fe bulk bcc, suggesting the absence of alloying with the matrices. The coercivity at 5K is much larger in Fe@Cr than in Fe@Ag as a result of the strong interaction between the Fe NPs and the Cr matrix. Temperature-dependent magnetization and ac-susceptibility measurements point out further evidence of the enhanced interparticle interaction in the Fe@Cr system. While the behaviour of Fe@Ag indicates the presence of weakly interacting magnetic monodomain particles with a wide distribution of blocking temperatures, Fe@Cr behaves like a superspin glass produced by the magnetic interactions between NPs.
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| 6. |
- Peddis, D., et al.
(författare)
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Memory and superposition in a superspin glass
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The non-equilibrium dynamics of the superspin glass state of a dense assembly of similar to 2 nm MnFe2O4 nanoparticles was investigated by means of magnetization, ac susceptibility and Mossbauer spectroscopy measurements and compared to the results of Monte Carlo simulations for a mesoscopic model that includes particles morphology and interparticle interactions. The zero-field cooled (ZFC), thermoremanent (TRM), and isothermal remanent magnetization (IRM) were recorded after specific cooling protocols and compared to those of archetypal spin glasses and their dimensionality. The system is found to display glassy magnetic features. We illustrate in detail, by a number of experiments, the dynamical properties of the low-temperature superspin glass phase. We observe that these glassy features are quite similar to those of atomic spin glasses. Some differences are observed, and interestingly, the non-atomic nature of the superspin glass is also reflected by an observed superspin dimensionality crossover. Monte Carlo simulations-that explicitly take into account core and surface contributions to the magnetic properties of these ultrasmall nanoparticles in direct contact, as well as interparticle interactions-evidence effects of the interplay between (intraparticle) core/surface exchange coupling and (interparticle) dipolar and exchange interactions.
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| 7. |
- Peddis, D., et al.
(författare)
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Studying nanoparticles' 3D shape by aspect maps : Determination of the morphology of bacterial magnetic nanoparticles
- 2016
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 191, s. 177-188
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic nanoparticles (MNPs) are widely investigated due to their potential use in various applications, ranging from electronics to biomedical devices. The magnetic properties of MNPs are strongly dependent on their size and shape (i.e., morphology), thus appropriate tools to investigate their morphology are fundamental to understand the physics of these systems. Recently a new approach to study nanoparticle morphology by Transmission Electron Microscopy (TEM) analysis has been proposed, introducing the so-called Aspect Maps (AMs). In this paper, a further evolution of the AM method is presented, allowing determination of the nanoparticles' 3D shape by TEM image. As a case study, this paper will focus on magnetite nanoparticles (Fe3O4), with a mean size of similar to 45 nm extracted from Magnetospirillum gryphiswaldense magnetostatic bacteria (MTB). The proposed approach gives a complete description of the nanoparticles' morphology, allowing estimation of an average geometrical size and shape. In addition, preliminary investigation of the magnetic properties of MTB nanoparticles was performed, giving some insight into interparticle interactions and on the reversal mechanism of the magnetization.
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| 8. |
- Vasilakaki, M., et al.
(författare)
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Memory effects on the magnetic behavior of assemblies of nanoparticles with ferromagnetic core/antiferromagnetic shell morphology
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:14, s. 140402-
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo simulations of the dynamic magnetic behavior of an assembly of ferromagnetic core/antiferromagnetic shell nanoparticles are reported and compared with the experimental results on a system of Co nanoparticles in Mn matrix. Memory effects on low-field zero-field-cooled magnetization curves have been investigated. Our simulations show that the memory effects increase with the concentration and that both the interface exchange coupling and the dipolar interparticle interactions contribute to the observed dynamic behavior. In particular the interface exchange interaction provides an additive source for the frustration of the system resulting in an enhancement of the memory effect. The numerical data reproduce well the experimental results confirming the glassy behavior of the investigated nanoparticle systems.
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| 9. |
- Vasilakaki, M., et al.
(författare)
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Monte Carlo study of the superspin glass behavior of interacting ultrasmall ferrimagnetic nanoparticles
- 2018
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 97:9
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Tidskriftsartikel (refereegranskat)abstract
- The magnetism of a dense assembly of ultrasmall ferrimagnetic nanoparticles exhibits unique features due to the combination of intraparticle and strong interparticle interactions. To model such system we need to account for the internal particle structure and the short-and long-range interparticle interactions. We have developed a mesoscopic model for the particle assembly that includes three spins (two for the surface and one for the core) for the description of each nanoparticle, interparticle dipolar interactions and the interparticle exchange interactions for the nanoparticles in contact. The temperature dependence of the observed exchange bias effect, due to exchange coupling at the interface between core/surface spins and the interparticle exchange coupling, and the zero-field-cooled-field-cooled magnetization vs temperature curves have been investigated using the Monte Carlo simulation technique with the implementation of the Metropolis algorithm. Our simulations reproduce well the experimental data of ultrasmall similar to 2-nm MnFe2O4 nanoparticles, confirming the close relationship between the superspin glass state and the exchange-bias effect in dense nanoparticle systems, owing to the interplay between the intraparticle structure and the interparticle effects.
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| 10. |
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