Different approaches to analyze the dipolar interaction effects on diluted and concentrated granular superparamagnetic systems

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Moscoso-Londono, O. ; Tancredi, P. ; Muraca, D. ; Mendoza Zelis, P. ; Coral, D. ; Fernandez van Raap, M. B. ; Wolff, U. ; Neu, V. ; Damm, C. ; de Oliveira, C. L. P. ; Pirota, K. R. ; Knobel, M. ; Socolovsky, L. M.

• Tipo de documento: Artigo Científico
• Fonte: Journal of Magnetism and Magnetic Materials; v. 428, p. 105-118, APR 15 2017.
• Citações Web of Science: 19

Resumo

Controlled magnetic granular materials with different concentrations of magnetite nanoparticles immersed in a non-conducting polymer matrix were synthesized and, their macroscopic magnetic observables analyzed in order to advance towards a better understanding of the magnetic dipolar interactions and its effects on the obtained magnetic parameters. First, by means of X-ray diffraction, transmission electron microscopy, small angle X-ray scattering and X-ray absorption fine structure an accurate study of the structural properties was carried out. Then, the magnetic properties were analyzed by means of different models, including those that consider the magnetic interactions through long-range dipolar forces as: the Interacting Superparamagnetic Model (ISP) and the Vogel-Fulcher law (V-F). In systems with larger nanoparticle concentrations, magnetic results clearly indicate that the role played by the dipolar interactions affects the magnetic properties, giving rise to obtaining magnetic and structural parameters without physical meaning. Magnetic parameters as the effective anisotropic constant, magnetic moment relaxation time and mean blocking temperature, extracted from the application of the ISP model and V-F Law, were used to simulate the zero-field-cooling (ZFC) and fieldcooling curves (FC). A comparative analysis of the simulated, fitted and experimental ZFC/FC curves suggests that the current models depict indeed our dilute granular systems. Notwithstanding, for concentrated samples, the ISP model infers that clustered nanoparticles are being interpreted as single entities of larger magnetic moment and volume, effect that is apparently related to a collective and complex magnetic moment dynamics within the cluster. (AU)

• Processo FAPESP: 14/26672-8 - Efeitos de interface e superfície em nanoheteroestruturas magnético-metálicas
• Beneficiário: Oscar Moscoso Londono
• Linha de fomento: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 11/01235-6 - Estudo de sistemas granulares magnéticos: efeitos de interações dipolares e de superfície em nanopartículas magnéticas e ferrogel
• Beneficiário: Diego Muraca
• Linha de fomento: Bolsas no Brasil - Pós-Doutorado