Anisotropic ferromagnetism in Fe _x Sn_1−x O₂ nanostructure arrays

Periodic arrays of Fe _x Sn_1−x O₂ nanostructures were fabricated by glancing angle sputter deposition onto self-assembled close-packed arrays of 200-nm-diameter polystyrene microspheres. After annealing at 873 K for 3 h, all the films were crystallized to rutile SnO₂ and maintained good thermal stability in the morphology. Compared with Fe _x Sn_1−x O₂ flat films, arrays of Fe _x Sn_1−x O₂ nanostructures possessed larger saturation magnetic moment and exhibited both perpendicular and in-plane magnetic anisotropy, resulting from the anisotropic morphology of Fe _x Sn_1−x O₂ nanostructures. The EPR signal originating from the oxygen vacancies significantly varied with the Fe concentration and reached the strongest at x = 0.059, which is consistent with the saturation magnetization. It demonstrates that the oxygen vacancies are an important factor for the ferromagnetism of Fe _x Sn_1−x O₂ films.