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Classical Magnetic models: towards an multi-scale approach

Classical Magnetic models : towards a multi-scale approach

Phenomenological magnetic models are able to bridge a gap between the microscopic magnetic properties and local organization of magnetic sites from a first part and the overall magnetic properties of bulk or nanosized materials from a second part.

In the case of Heisenberg model, the magnetic Hamiltonian is governed by few critical parameters, namely the magnetic moments of sites, the exchange energy between neighbors, the volume anisotropy constant and for finite size objects, the surface anisotropy constant and interface anisotropy constants.

Accuracy of the results emerging from the classical model is then intimately related to the theoretical or experimental determination of the underlying magnetic parameters and microscopic site organization of the system. This level of knowledge is not necessarily fulfilled in the case of complex structures or unusual compounds. Using a numeric multi-scale approach coupling ab-initio, molecular dynamics and Heisenberg simulations, access to a finer level of description. From one part the use of molecular dynamics simulation, permits to relax the structure of nano-sized or bulk systems and then to reproduce the magnetic sites position and distribution in a more realistic way. From another side, adjustments of ab-initio calculations and Heisenberg model on a large statistical sample of representative local environments allow us to determine the microscopic magnetic parameters.

 

Left: Influence of dopamine functionalization on magnetic properties. Right: Influence of structure relaxation on magnetic properties

Related papers

  • Brymora and F. Calvayrac, Surface anisotropy of iron oxide nanoparticles and slabs from first principles: Influence of coatings and ligands as a test of the Heisenberg model, Journal of Magnetism and Magnetic Materials, 2017, 434, 14–22.
  • Sayed, Y. Labaye, R. Sayed Hassan, F. El Haj Hassan, N. Yaacoub and J. M. Greneche, Size and thickness effect on magnetic structures of maghemite hollow magnetic nanoparticles, Journal of Nanoparticle Research, 2016, 18, 279.
  • Nehme, Y. Labaye, R. Sayed Hassan, N. Yaacoub and J. M. Greneche, Modeling of hysteresis loops by Monte Carlo simulation, AIP Advances, 2015, 5, 127124.

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