Oxygen vacancy and dilute ferromagnetism of ZnGa2O4 doped with Co at the octahedral site

Abstract

We report magnetism and structure of a diluted magnetic semiconductor Zn[Ga0.97Co0.03]2O4 preferentially doped with Co ions in the octahedral site of zinc gallate ZnGa2O4. Zn[Ga0.97Co0.03]2O4 has a small ferromagnetic component superimposed on a large paramagnetic contribution to the magnetization at room temperature, whereas ZnGa2O4 is diamagnetic. The X-ray powder diffraction confirms that both ZnGa2O4 and Zn[Ga0.97Co0.03]2O4 have a normal spinel structure (space group Fd-3m) without any impurity phases. From X-ray absorption fine structure measurements we find the following features in Zn[Ga0.97Co0.03]2O4; all of the Co dopants occupy the octahedral site, about half of which are divalent; around the Co cations there exist the oxygen vacancies and the local distortion of shrink in pair distance, while the local structure around Zn and Ga ions coincides with that expected from the X-ray diffraction. These features suggest that the local disorder including oxygen vacancies and distortions only around Co ions plays an important role in stabilizing the ferromagnetic order between some Co ions in Zn[Ga0.97Co0.03]2O4.