Magnetism induced by capping of non-magnetic ZnO nanoparticles

Magnetism of 10 nm size capped nanoparticles, NPs, of non-magnetic ZnO is analysed in terms of the surface band since, as magnetic dichroism analysis has pointed out, impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. Due to the nanometric scale of the particles the kinetic energy spectrum of the surface states can be considered as discrete. Therefore, the magnetic polarisation cannot be easily induced by pumping electrons to energy levels above the Fermi energy. It is in the Fermi level itself, generally unfilled, that develops a spontaneous magnetic moment similarly to that induced by Hund rules in unfilled atomic orbitals. It is shown, however, that the total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 102 or 103 Bohr magnetons.