Surface anisotropy of a Fe3O4 nanoparticle: A simulation approach

Abstract:

On the basis of a three-dimensional classical Heisenberg model with nearest magnetic neighbor interactions, and using a Monte Carlo-Metropolis dynamics, we study the magnetic behavior of a 5 nm diameter magnetite nanoparticle as a function of temperature. The nanoparticle is built by taken into account the inverse spinel structure of a stoichiometric magnetite, the valence of the iron ions (Fe³⁺<inf>A</inf>, Fe³⁺<inf>B</inf>, Fe²⁺<inf>B</inf> where A and B stand for tetrahedral and octahedral sites, respectively) as well as the different involved coordination numbers and superexchange integrals. The employed Hamiltonian includes coupling interactions between Fe ions through the integrals J<inf>AA</inf>, J<inf>AB</inf> and J<inf>BB</inf>, a Néel's surface anisotropy term applied to surface ions, and cubic magnetocrystalline anisotropy for those ions belonging to the core of the nanoparticle. Results reveal a strong influence of surface anisotropy, depending on its sign and magnitude, upon the total magnetization at low temperatures. Such results, which are summarized in a proposal of phase diagram, reveal the onset of spin structures different from a single-domain state. Differences in the thermal behavior respect to a bulk magnetite are also addressed and discussed. © 2007 Elsevier B.V. All rights reserved.

Año de publicación:

2007

Keywords:

• Nanoparticles
• Magnetite
• Monte Carlo
• Surface anisotropy

Fuente:

scopus