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

## TL;DR

This study uses first-principles calculations to analyze the surface magnetic anisotropy of iron oxide nanoparticles and slabs, examining the effects of coatings and ligands on magnetic behavior and testing the Heisenberg model's applicability.

## Contribution

It introduces a method to estimate surface anisotropy from ab initio data and improves the Heisenberg model by adjusting anisotropies for hybrid oxide systems.

## Key findings

- Surface anisotropy values align with experimental estimates.
- Ligands and coatings reduce the Heisenberg model's accuracy.
- Modified anisotropies enhance the model's description of hybrid systems.

## 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.