Surface anisotropy of iron oxide nanoparticles and slabs from first principles: Influence of coatings and ligands as a test of the Heisenberg model

Abstract

We performed ab initio computations of the magnetic properties of simple iron oxide clusters and slabs. We considered an iron oxide cluster functionalized by a molecule or glued to a gold cluster of the same size. We also considered a magnetite slab coated by cobalt oxide or a mixture of iron oxide and cobalt oxide. The changes in magnetic behavior were explored using constrained magnetic calculations. A possible value for the surface anisotropy was estimated from the fit of a classical Heisenberg model on ab initio results. The value was found to be compatible with estimations obtained by other means, or inferred from experimental results. The addition of a ligand, coating, or of a metallic nanoparticle to the systems degraded the quality of the description by the Heisenberg Hamiltonian. Proposing a change in the anisotropies allowing for the proportion of each transition atom we could get a much better description of the magnetism of series of hybrid cobalt and iron oxide systems.

Convoluted Magnetoresistance and Magnetic Reversal Processes in Ni–Fe Segmented Cylindrical Nanodots with Tunable Size and Composition for Technological Applications

“…It is worth noting that other authors have provided alternative methods, based on non‐collinear spin DFT calculations, to successfully calculate exchange constants at a magnetic interface with comparable results. [ 6 ]…”

“…It is worth noting that other authors have provided alternative methods, based on non-collinear spin DFT calculations, to successfully calculate exchange constants at a magnetic interface with comparable results. [6] Thus, the so-obtained exchange couplings (J) coming from the DFT approach are computed for Fe-Fe (represented as J Fe−Fe−DFT ), Ni-Ni (J Ni-Ni-DFT ) and Fe-Ni (J Fe-Ni-DFT ). Then, since the values for bulk Fe (J Fe-Fe-MC ) and bulk Ni (J Ni-Ni-MC ) that work well in MC simulations are known, the Fe-Ni exchange coupling at the interface (J Fe-Ni-MC ) are computed.…”

“…In the very recent years, attention from both the theoretical and experimental viewpoints has turned toward nanostructures composed by mixed elements. In fact, some researchers have used First Principles approaches as well as Monte Carlo (MC) methods and Heisenberg models with good results to study the interactions taking place at interfaces, [ 6–10 ] in some cases, with locally variable surface anisotropies to account for the experimental results. Also, systems composed by varied phases, due to their peculiar properties offer amazing advantages for applications in fields such as sensors, high density magnetic data storage, nanoscale electronics, and spintronics.…”

Laser spectroscopy of finite size and covering effects in magnetite nanoparticles

“…The experimental data presented can be interpreted on the basis of several different methods: various approximations in the Ising or Heisenberg models, quantum-chemical and first-principle calculations [22]. In the variety of these approaches, the most suitable approximation is regarded the core-shell model [5] which is a modification of the Weizsäcker model used for the analysis of specific characteristics of complex nucleus.…”

Role of surface spins on magnetization of Cr2O3 coated γ-Fe2O3 nanoparticles

“…γ Fe 2 O 3 nanoparticles are ferrimagnetic in nature and exhibit spinel structure along with cation vacancies at octahedral sites. These vacancies along with competing surface inter actions can lead to surface spins disorder and spin glass behavior in γ Fe 2 O 3 nanoparticles [9]. Fiorani et al [10] studied the dynamical and static properties of γ Fe 2 O 3 nanoparticles which are governed by sur face effects and interparticle interactions.…”