Influence of oxygen vacancies on magnetic and transport properties of thin Zn_1-xCo_xO_y films

The features of the structural, transport and magnetic properties of thin Zn_1-xCo_xO_y films (x=0-0.45), fabricated on С-sapphire substrates by the pulsed laser deposition method are studied. It is found that the transport and ferromagnetic properties of the wurtzite Zn_1-xCo_xO_y films nonmonotonously depend on Co concentration at room temperature. For the Zn_0.87Co_0.13Oy film, the strongest ferromagnetic signal is observed that is caused by formation of the greatest number of metallic Co clusters. A further increase of doping impurity concentration in the films leads to the oxidation of metallic Co and formation of the paramagnetic Co₃O₄ phase, in consequence of which the ferromagnetic signal subsides.