Defect driven magnetism in doped SnO2 nanoparticles: Surface effects

Magnetism and energetics of intrinsic and extrinsic defects and defect clusters in bulk and surfaces of SnO2 is investigated using first-principles to understand the role of surfaces in inducing magnetism in Zn doped nanoparticles. We find that Sn vacancies induce the largest magnetic moment in bulk and on surfaces. However, they have very large formation energies in bulk as well as on surfaces. Oxygen vacancies on the other hand are much easier to create than VSn, but neutral and VO+2 vacancies do not induce any magnetism in bulk as well as on surfaces. VO+1 induce small magnetism in bulk and on (001) surfaces. Isolated ZnSn defects are found to be much easier to create than isolated Sn vacancies and induce magnetism in bulk as well on surfaces. Due to charge compensation, ZnSn+VO defect cluster is found to have the lowest formation energy amongst all the defects; it has a large magnetic moment on (001), a small magnetic moment on (110) surface and non-magnetic in bulk. Thus, we find that ZnSn and ZnSn+VO defects on the surfaces of SnO2 play an important role in inducing the magnetism in Zn-doped SnO2 nanoparticles.