Low-energy properties of two-dimensional magnetic nanostructures: interparticle interactions and disorder effects

Abstract

The low-energy properties of two-dimensional ensembles of dipole-coupled magnetic nanoparticles are studied as function of structural disorder and particle coverage. Already small deviations from a square particle arrangement lift the degeneracies of the microvortex magnetic configuration, and result in a strongly noncollinear magnetic order of the particle ensemble. The energy distribution of metastable states is determined. For a low degree of disorder a strongly asymmetric shape with a pronounced peak of the ground state energy results. In contrast, for a strong disorder a Gaussian-like distribution is obtained. The average dipole coupling energy ${\bar{E}}_{\mathrm{dip}}$ decreases with increasing structural disorder. The role of vacancies has been studied for a square particle array by determining the angular distribution of the preferred microvortex angle as function of the vacancy concentration. Indications for a preferred angular direction along the axial as well as along the diagonal directions of the square array are revealed. A corresponding investigation for disturbed square arrays results in a different angular distribution. The effect of dipole-quadrupole corrections resulting from the finite size of the particles is quantified.

arXiv comment23 pages, 7 figures

References in corpus (4)

• Absence of spontaneous magnetic order at non-zero temperature in one- and two-dimensional Heisenberg and XY systems with long-range interactions
• Dipolar interaction between two-dimensional magnetic particles
• Non-equilibrium dynamics in an interacting nanoparticle system
• Dipole coupling induced magnetic ordering in an ensemble of nanostructured islands

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• Scaling behavior of the dipole coupling energy in two-dimensional disordered magnetic nanostructures
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• Vortex fluctuations and freezing of dipolar-coupled granular moments in thin ferromagnetic films