Room-temperature ferromagnetism and morphology evolution of SnO2 flower-like microparticles by Zn-doping

We report on the growth of undoped and Zn-doped flower-like microparticles, which are constituted of SnO2 acicular nanoparticles (NPs) aggregated by one of their ends. NPs were synthesized by the hydrothermal method. The morphology of the NPs progressively changes from truncated rods to sharp needles by the effect of Zn doping. This morphology evolution is attributed to an increase of the surface free energy of the NPs' facets and to a modification of the growth front direction. Undoped samples exhibit a very low magnetization attributed to single positive charged oxygen vacancies,V-O(1+), while Zn-doped samples exhibit ferromagnetic ordering due to Zn atoms in Sn substitutional positions (Zn-Sn). Thermal treatment under reducing atmosphere leads to the creation of an excess of V-O conducting to a reduction of the magnetization, demonstrating that ferromagnetism in Zn-doped SnO2 NPs is attributed to Zn-Sn defects and to the octahedrally coordinated oxygen atoms.