N.C.S.R. "Demokritos"

Research

Department of Materials Science

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Magnetic Behaviour of Nanoparticle Assemblies

Assemblies of magnetic nanoparticles (NPs) are met most often in naturally occurring systems and in man-made structures such as granular solids, patterned structures, self-organized arrays. Interparticle interactions (magnetostatic, exchange) become of major importance as the demand for higher density in magnetic storage leads to decreased interparticle spacing. Interparticle interactions have inevitable effects on the global magnetic behavior of a sample and introduce a rich structure to the phase diagram of the assembly as the packing density increases. The magnetic domain structure is rather complex due to competition between the short range exchange forces acting between nanoparticles "in-contact" and the long range dipolar interactions. In this project we investigate the role of interactions in random and ordered NP assemblies within the framework of the Coherent Rotation model in the case of simple ferromagnetic nanoparticles. In the case of composite nanoparticles, we have developed a new model that takes into accound the nanoparticle microstructure. We use classical spin Hamiltonians and Monte Carlo simulations to obtain the macroscopic magnetic properties (isothermal hysteresis loop, field-cooled and zero-field-cooled magnetization, Henkel plots, etc) of the assemblies. Furthermore, the thermally activated magnetization relaxation is studied by numerical simulations and the Fokker-Planck equation.

Department of Materials Science, N.C.S.R. "Demokritos", 153 10 Aghia Paraskevi, Attiki, phone: +30 210 6503381, fax: +30 210 6519430
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