Surface modification of Co-doped ZnO nanocrystals and its effects on the magnetic properties

A series of chemically prepared Co2+-doped ZnO colloids has been surface modified either by growing shells of ZnSe or by the in situ encapsulation in poly styrene . The surface modification effects using these two distinct chemical strategies on the magnetic properties of the nanocrystals were probed by electron paramagnetic resonance EPR . Structural characterization by means of x-ray diffraction and transmission electron microscopy gave no evidence of second phase formation within the detection limits of the used equipment. The EPR analysis was carried out by simulations of the powderlike EPR spectra. The results confirm that in the core of these nanocrystals Co was incorporated as Co2+, occupying the Zn2+ sites in the wurtzite structure of ZnO. Additionally we identify two Co signals stemming from the nanocrystals’ shell. The performed surface modifications clearly change the relative intensity of the EPR spectrum components, revealing the core and shell signals

Magnetic and structural properties basic solid state physics of transition metal doped zinc-oxide nanostructures

We report on the magnetic and structural properties of two types of nanostructures doped with Co or Mn, namely, ZnO nanowires and colloidal ZnO nanocrystals. Electron paramagnetic resonance (EPR) spectra have been measured and analysed to extract information on the incorporation of the ions in the lattice. A detailed analysis by means of simulations of the experimental EPR spectra confirms that the transition metal (TM) ions were mainly incorporated as TM2+, occupying the Zn2+ sites in the wurtzite structure of ZnO. Furthermore, for both types of nanostructures, the EPR spectra are composed of more than one signal, revealing locally distorted environments or core-shell structures, proved by surface modifications via inorganic coatings