Ferromagnetic glass on the base of aggregates of Ni amorphous nanogranules

Journal article (2011)

Authors

D. S. Ilyushenkov Russian Academy of Sciences
V. I. Kozub Russian Academy of Sciences
I. N. Yassievich Russian Academy of Sciences
T. T. Nguyen Universiteit van Amsterdam
E.H. Brück Universiteit van Amsterdam
Affiliation
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Amorphous monodisperse nanoparticles Ferromagnetic glass Magnetic properties of nanoparticles
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Published Date

2011

Language

English

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Abstract

We have studied theoretically (including computer simulations) magnetic properties of aggregates of ferromagnetic amorphous nanogranules in the presence of direct exchange between the neighboring granules and random anisotropy fields. We show that such a system can be considered as ferromagnetic glass. We demonstrate (basing on analytical considerations as well as on the results of numerical simulations) that the system is decomposed to clusters or domains with nearly collinear orientation of magnetization. The size of the domains depends on the ratio of the exchange interaction and random anisotropy. For quasi-2D structures we predict that the dipoledipole interactions between the granules lead to a formation of magnetic vortices. Moreover, the computer simulations also reproduce the puzzling increase of the thermoremanent magnetization observed experimentally, which is expected to be a result of a temperature-dependent decrease in the anisotropy (or a temperature-dependent increase in the exchange). We also consider the structures with weak intergranular exchange and show that they are characterized by the presence of two critical temperatures.