Exploring d0 magnetism in doped SnO2–a first principles DFT study

• Systematic study of d0 magnetism in SnO2 doped with group 1A (Li, Na, K) and group 2A (Be, Mg, Ca).
• Sufficient hole density required for group 2A impurity to induce FM, a finding not reported earlier.
• For room temperature FM 3 holes per defect not a necessary criterion.
• The system needs a critical hole concentration to activate FM by satisfying Stoner criterion.

In search of d0 magnetism, the magnetic behavior of SnO2 with cation substitution from group1A (Li, Na, K) and group 2A (Be, Mg, Ca) elements has been systematically studied using Density Functional Theory (DFT). While an impurity from group 1A elements switches on ferromagnetism at a lower concentration itself, sufficient hole density is required for a group 2A impurity to create a spontaneous spin polarized ground state, a finding that has not been reported in earlier investigations. Our DFT results predict for the first time that impurities from group 2A (Mg, Ca) in SnO2 can promote room temperature ferromagnetism. Further, the emergence of ferromagnetism due to doping from group 1A elements, which injects three holes per defect, has been mapped successfully onto a modified Hubbard model from the literature. Doping of a single Na atom in the supercell (concentration 6.25 at%) makes the system ferromagnetic, with a magnetic moment close to 3.0 μB per defect, and a Curie temperature of 815 K, obtained in the mean field approximation. This agrees closely with a model prediction of 750 K. Finally, the triggering of ferromagnetism by an impurity atom from group 2A, which adds two holes per defect in the system, implies that the prescription of three holes per defect given in the literature is not a necessary criterion for hole induced ferromagnetism. Rather, the analysis of the density of states and ferromagnetic coupling indicate that the system needs a critical hole concentration to activate ferromagnetism, by pushing the Fermi level inside the valence band in order to satisfy the Stoner criterion.

Spin density (Δρ=ρ↑−ρ↓) shown in yellow color mainly concentrated on the first shell O atoms around the impurity (a)Li, (b)Na, (c) K for isovalue 0.2e (d) K for isovalue 0.1.Figure optionsDownload as PowerPoint slide