Abstract
Single domain magnetic nanoparticles (MNP) interacting through dipolar interactions (DDI) in addition to the magnetocrystalline energy may present a low temperature ferromagnetic (SFM) or spin glass (SSG) phase according to the underlying structure and the degree of order of the assembly. We study, from Monte Carlo simulations in the framework of the effective one-spin or macrospin models, the case of a monodisperse assembly of single domain MNP fixed on the sites of a perfect lattice with fcc symmetry and randomly distributed easy axes. We limit ourselves to the case of a low anisotropy, namely the onset of the disappearance of the dipolar long-range ferromagnetic (FM) phase obtained in the absence of anisotropy due to the disorder introduced by the latter.
Highlights
The physics of nanoscale magnetic materials is still a very active field of research both in view of the potential applications, especially in nanomedicine [1], and from the fundamental point of view [2, 3]
The fundamental aspects are all the more important that magnetic nanoparticles (MNP) can be synthesized in a wide range of size and shapes and their assemblies obtained with different structures: colloidal suspensions, or ferrofluids embedded in non-magnetic materials where one can tune the interparticle interactions through the concentration, or as powders
Due to frustration effects, according to whether the MNP are arranged or not with a long-range order at high concentration, a ferromagnetic or a spin glass state is expected at a low temperature [3, 7]
Summary
The physics of nanoscale magnetic materials is still a very active field of research both in view of the potential applications, especially in nanomedicine [1], and from the fundamental point of view [2, 3]. In the limiting case of an infinite magnitude of the MAE, the DHS on a lattice reduces to the dipolar Ising model, where the exchange coupling constants Jij follow the dipolar energy form for moments aligned on the easy axes.
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