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4. On the detection of surface spin freezing in iron oxide nanoparticles and its long-term evolution under ambient oxidation.

Author

Ghoshani, M, Sánchez, E H, Lee, S S, Singh, G, Yaacoub, N, Peddis, D, Mozaffari, M, Binns, C, De Toro, J A, and Normile, P S

Subjects
LONG-Term Evolution (Telecommunications), MAGNETITE, IRON oxide nanoparticles, MOSSBAUER spectroscopy, MAGHEMITE, FREEZING, OXIDATION
Abstract

Exchange bias (EB) effects linked to surface spin freezing (SSF) are commonly found in iron oxide nanoparticles, while signatures of SSF in low-field temperature-dependent magnetization curves have been much less frequently reported. Here, we present magnetic properties of dense assemblies of similar-sized (∼8 nm diameter) particles synthesized by a magnetite (sample S1) and a maghemite (sample S2) method, and the influence of long-term (4 year) sample aging under ambient conditions on these properties. The size of the EB field of the different sample (fresh or aged) states is found to correlate with (a) whether a low-temperature hump feature signaling the SSF transition is detected in out-of-phase ac susceptibility or zero-field-cooled (ZFC) dc magnetization recorded at low field and with (b) the prominence of irreversibility between FC and ZFC curves recorded at high field. Sample S1 displays a lower magnetization than S2, and it is in S1 where the largest SSF effects are found. These effects are significantly weakened by aging but remain larger than the SSF effects in S2, where the influence of aging is considerably smaller. A non-saturating component due to spin disorder in S1 also weakens with aging, accompanied by, we infer, an increase in the superspin and the radius of the ordered nanoparticle cores. X-ray diffraction and Mössbauer spectroscopy provide indication of maghemite-like stoichiometry in both aged samples as well as thicker disordered particle shells in aged-S1 relative to aged-S2 (crystallographically-disordered and spin-disordered according to diffraction and Mössbauer, respectively). The pronounced diminution in SSF effects with aging in S1 is attributed to a (long-term) transition, caused by ambient oxidation, from magnetite-like to maghemite-like stoichiometry, and a concomitant softening of the spin-disordered shell anisotropy. We assess the impact of this anisotropy on the nature of the blocking of the nanoparticle superspins. [ABSTRACT FROM AUTHOR]

Published
2021
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9. Ferromagnetic Mn-doped Si0.3Ge0.7nanodots self-assembled on Si(100)

Author

De Padova, P, primary, Olivieri, B, additional, Mariot, J-M, additional, Favre, L, additional, Berbezier, I, additional, Quaresima, C, additional, Paci, B, additional, Generosi, A, additional, Rossi Albertini, V, additional, Cricenti, A, additional, Ottaviani, C, additional, Luce, M, additional, Testa, A M, additional, Peddis, D, additional, Fiorani, D, additional, Scarselli, M, additional, De Crescenzi, M, additional, Heckmann, O, additional, Richter, M C, additional, Hricovini, K, additional, and d’Acapito, F, additional

Published
2012
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17. Magnetic mesoporous silica nanostructures: investigation of magnetic properties

Author

Gianni Barucca, Sawssen Slimani, Patrizia Imperatori, Armida Sodo, Ludovica Ruggiero, Alessandro Talone, Davide Peddis, Maria Antonietta Ricci, Talone, A., Ruggiero, L., Slimani, S., Imperatori, P., Barucca, G., Ricci, M. A., Sodo, A., and Peddis, D.

Subjects
magnetic nanoparticles, Materials science, magnetic nanoparticle, Nanoparticle, Bioengineering, 02 engineering and technology, 010402 general chemistry, 01 natural sciences, Magnetization, chemistry.chemical_compound, nanocomposites, mesostructured silica, General Materials Science, Electrical and Electronic Engineering, Mechanical Engineering, General Chemistry, Mesoporous silica, 021001 nanoscience & nanotechnology, 0104 chemical sciences, Magnetic anisotropy, chemistry, Chemical engineering, Mechanics of Materials, Remanence, Magnetic nanoparticles, 0210 nano-technology, Mesoporous material, Iron oxide nanoparticles
Abstract

Magnetic mesoporous silica (MS) nanocomposites provide the possibility of generating multi-functional objects for application in different technological areas. This paper focuses on the magnetic properties of nanocomposites constituted by spinel iron oxide nanoparticles (magnetic nanoparticles (MNPs), < D > ≈ 8-9 nm) embedded in an MS matrix. The mesoporous structure of the silica matrix and the presence of the nanoparticles inside clearly emerge from transmission electron microscopy (TEM) measurements. Low temperature (5 K) field-dependent magnetization measurements reveal saturation magnetization (MS ) close to bulk value (M S bulk ∼ 90 emu g-1) for both MNPs and MNP/MS nanocomposites, indicating that the presence of silica does not affect the magnetic features of the single MNPs. Moreover, the dependence of the remanent magnetization on field (i.e. δM plots) at low temperature has shown a small but evident decrease of interaction in an MNP/MS sample with respect to MNP samples A m2 Kg-1. Finally, a partial orientation of the easy axis is observed when the MNPs are embedded in the silica matrix.

Published
2020

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