Tuning the magnetic properties of oleic-acid-coated cobalt ferrite nanoparticles by varying the surfactant coverage

Abstract

Organic coatings on magnetic nanoparticles are extensively used in various applications. As demonstrated recently, these coatings affect the magnetic behavior of the nanoparticles. The modification of the magnetic properties of the nanoparticles and nanoparticle assemblies as the percentage of the oleic acid (OA) coverage of a cobalt ferrite nanoparticle increases, is investigated numerically using a multiscale modeling approach that combines density functional theory (DFT) and Monte Carlo simulations. The DFT calculations show that the increase in OA coverage results in a monotonic decrease of the mean magneto-crystalline anisotropy and in a reduction of the atomic magnetic moments and the exchange coupling constants in the nanoparticle. These effects are attributed to the gradual recovery of the bulk spinel structure at the coated surface, as the OA coverage increases. Input from the DFT calculations is used in the mesoscopic modeling for the study of the magnetic behavior of an assembly of these nanoparticles by employing the Monte Carlo simulations technique. The results demonstrate that despite the decrease of magnetic anisotropy, the coercive field increases with the increase in percentage of OA coverage in the assembly, in agreement with experimental findings. This study suggests the possibility of tailoring the magnetic properties of cobalt ferrite nanoparticles for high-performance applications by varying the organic coating concentration.