2018-Sustainable Industrial Processing Summit
SIPS2018 Volume 5. Zehetbauer Intl. Symp. / SISAM
| Editors: | F. Kongoli, S. Kobe, M. Calin, J.-M. Dubois, T. Turna |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2018 |
| Pages: | 154 pages |
| ISBN: | 978-1-987820-90-4 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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Overview of Magnetic Nanoparticle Systems
Marcelo Knobel1;1UNIVERSITY OF CAMPINAS (UNICAMP), Campinas, Brazil;
Type of Paper: Regular
Id Paper: 343
Topic: 42
Abstract:
Studies of magnetic nanoparticle systems have attracted much interest in the past few years, owing to their fundamental interest and technological applications [1]. In particular, the correlation of parameters such as size, morphology, crystalline structure, and shape of the particles with the resulting magnetic properties has been thoroughly investigated, but many questions remain to be answered. Besides the effect of grain size distribution— which strongly affects the magnetic response of the system— there are important factors that need to be controlled, such as the surface of the particles (both roughness and composition gradient), the shape, and the phases formed within the nanograins.
Another crucial point is the role played by magnetic interactions among the magnetic entities. This subject has been extensively studied from both experimental and theoretical approaches, but even now it is not clear how the dipole-dipole interactions can affect the macroscopic magnetic response of the system. Many different, often conflicting models have been applied to explain the experimental data on interacting magnetic nanoparticle systems. Consequently, there has been a considerable discussion about the existence of significant collective effects in magnetic nanoparticle systems, and several speculations regarding a spin-glass-like phase at low temperatures on dipole-dipole interacting systems. With the inclusion of dipolar interactions the problem becomes complex, and it is usually solved by means of some approximation. One of the most used methods to investigate the role of interactions has been Monte Carlo simulations. In addition, novel phenomenological approaches have proposed analytical models that explicitly take into account the correlation arising from the dipolar interactions on nearly superparamagnetic systems.
As a matter of fact, the lack of close-to-ideal samples (with controlled grain size, shape, etc.) hindered more systematic experimental studies. In turn, the absence of perfectly reliable experimental data did not allow a consistent comparison with theoretical models and/or computer simulations.
A brief review on the existing models will be given, and new experimental results on sets of sputtered and chemically grown nanocrystalline samples will be shown. Systematic studies as a function of grain size, distance among magnetic entities will be analysed through the different theoretical models, demonstrating the great importance of dipolar interactions on the magnetic properties of granular systems.