Cobalt doped ZnO quantum dots in a monolayer: do the bands depend on the alignment of the magnetic domain?

Abstract

We show that energy of conduction and valence band-edges of ferromagnetic quantum dots in a monolayer changes when the nanocrystals' magnetic moments are aligned or oriented. Here we characterize a monolayer of cobalt-doped ZnO nanoparticles with scanning tunnelling microscopy. We observed that when their magnetic domains are aligned or oriented, transport gap of the quantum dots decreases. The decrease in the gap is primarily due to an increase in valence band-edge energy. We vary the content of cobalt in the doped-nanoparticles and also the degree of alignment of their magnetic moments. Measurements of band-edges and transport gap of such nanocrystals in a monolayer support our observation. The results hence provide a new route to control transport gap and band-edge energies of ferromagnetic quantum dots through the process of alignment of magnetic domains of the nanocrystals.