Conditions determining the morphology and nanoscale magnetism of Co nanoparticles: Experimental and numerical studies

TL;DR

This study explores how reaction conditions influence the shape and magnetic properties of cobalt nanoparticles, combining experimental synthesis, structural analysis, and numerical modeling to understand their morphology and nanoscale magnetism.

Contribution

It provides new insights into how diffusivities of Co and oxygen affect nanoparticle morphology and magnetic behavior, supported by experimental and numerical approaches.

Findings

Diffusivities of Co and oxygen determine nanoparticle growth and shape.

Exchange coupling affects magnetic hysteresis proportional to shell thickness.

Hollow nanoparticles exhibit hysteresis above 300 K due to surface anisotropy.

Abstract

Co-based nanostructures ranging from core-shell to hollow nanoparticles were produced by varying the reaction time and the chemical environment during the thermal decomposition of Co2(CO)8. Both structural characterization and kinetic model simulation illustrate that the diffusivities of Co and oxygen determine the growth ratio and the final morphology of the nanoparticles. Exchange coupling between Co and Co-oxide in core/shell nanoparticles induced a shift of field-cooled hysteresis loops that is proportional to the shell thickness, as verified by numerical studies. The increased nanocomplexity when going from core/shell to hollow particles, also leads to the appearance of hysteresis above 300 K due to an enhancement of the surface anisotropy resulting from the additional spin-disordered surfaces.