Zn0.75 Co0.25 O films are fabricated via reactive electron beam evaporation.The influence of growth temperature on the microstructural,optical and magnetic properties of Zn0.75 Co0.25 O films is investigated by using x-ray diffraction,selected area electron diffraction,field emission scanning electron microscope,high resolution transmitting electron microscope,photoluminescence(PL),field dependent and temperature dependent DC magnetization,and x-ray photoelectron spectroscopy(XPS).It is shown that Zn 0.75 Co 0.25 O films grown at low temperatures(250-350 C) are of single-phase wurtzite structure.Films synthesized at 300 or 350 C reveal room temperature(RT) ferromagnetism(FM),while superparamagnetism for 250 C fabricated films is found above 56 K.PL and XPS investigations show favour towards the perspective that the O-vacancy induced spin-split impurity band mechanism is responsible for the formation of RT FM of Zn0.75 Co0.25 O film,while the superparamagnetism of 250 C fabricated film is attributed to the small size effect of nanoparticles in Zn0.75 Co0.25 O film.
