Fe nanoparticles embedded in MgO crystals

Iron nanoparticles embedded in MgO single crystals were synthesized by high temperature Fe+ implantation with energy of 100 keV and fluences varying from 3×10E16 to 3×10E17 ions/cm-2. Complex investigations of structural and magnetic properties of Fe nanoparticles have been performed using magnetometry, x-ray diffraction, electron microscopy and Moessbauer spectroscopy, as well as theoretical modeling of magnetization of bistable magnetic systems.
It has been found that at the low implantation fluences superparamagnetic Fe nanoparticles were created that finally were attributed to alpha-Fe coexisting with non-magnetic gamma-Fe, while implantation with high fluences causes formation of ferromagnetic alpha-Fe particles. Post implantation annealing at 800 ºC in high vacuum results in size increase of the gamma-Fe particle’s simultaneously reducing internal lattice strain. Annealing at 800 ºC under 1 GPa hydrostatic pressure limits dimension of superparamagnetic nanoparticles significantly increasing their concentration.
Theoretical simulations of irreversible magnetization processes, performed within the framework of generalized Preisach model, show a strong correlation between the spontaneous magnetization, coercive field and dimension of nanoparticles. The model allows us to define the anisotropy effects and thermal fluctuation effects, which provides the detailed description of temperature behavior of magnetization.