1999/10/25 by H. Kachkachi, M. Nogues, M. Noguès +3 · 2 citations
Engineering · Physics and Astronomy · #Characterization and Applications of Magnetic Nanoparticles #Magnetic properties of thin films #Theoretical and Computational Physics #cond-mat.mtrl-sci
paper · pdf · doi:10.1016/s0304-8853(00)00390-5
published as J. Magnetism and Magnetic Materials 221 (2000) 158-163 · 6 pages of RevTex including 4 Figures, invited paper to 3rd EuroConference on Magnetic Properties of Fine Nanoparticles, Barcelona, October 99
arxiv created 1999/10/25 · openalex publication_date 2000/11/01 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We study the finite-size and surface effects on the thermal and spatial behaviors of the magnetisation of a small magnetic particle. We consider two systems: 1) A box-shaped isotropic particle of simple cubic structure with either periodic or free boundary conditions. This case is treated analytically using the isotropic model of D-component spin vectors in the limit D→ ∞, including the magnetic field. 2) A more realistic particle (γ-Fe2O3) of ellipsoidal (or spherical) shape with open boundaries. The magnetic state in this particle is described by the anisotropic classical Dirac-Heisenberg model including exchange and dipolar interactions, and bulk and surface anisotropy. This case is dealt with by the classical Monte Carlo technique. It is shown that in both systems finite-size effects yield a positive contribution to the magnetisation while surface effects render a larger and negative contribution, leading to a net decrease of the magnetisation of the small particle with respect to the bulk system. In the system 2) the difference between the two contributions is enhanced by surface anisotropy. The latter also leads to non saturation of the magnetisation at low temperatures, showing that the magnetic order in the core of the particle is perturbed by the magnetic disorder on the surface. This is confirmed by the profile of the magnetisation.