Effects of vacancy and lattice distortion on ferromagnetism in sputtered epitaxial Sn1−xKxO2 films

•(100)-orientated Sn1−xKxO2 films were deposited on the (0001) surface of sapphire.•Three distinct symmetry equivalent in-plane orientations were observed.•The ferromagnetism enhances monotonously with doping, which is established through p–p coupling interaction.•The lattice distortion will disturb the arrangement of the electrons and can be remitted by post-thermal treatment.

Structures, optical and magnetic properties of epitaxial Sn1−xKxO2 films were investigated experimentally. Three distinct symmetry equivalent in-plane orientations were observed between the film and substrate. The ferromagnetism enhances monotonously with doping and the largest saturation magnetization is 7.88 emu/cm3 in Sn0.92K0.08O2 film. Generated K interstitials may give rise to a symmetry-lowering distortion of the surrounding lattice. The alignment of magnetic moments in Sn1−xKxO2 films is established through p–p coupling interaction between the impurity p states and host p states. The lattice distortion induced by K at both interstitial site and substitution site will disturb the arrangement of the electrons and can be remitted by post-thermal treatment.