Optical and magnetic properties of cobalt doped TiN thin films grown by RF/DC magnetron sputtering

Here we report the study of cobalt doped titanium nitride thin films grown by reactive co-sputtering of cobalt and titanium targets in the presence of argon and nitrogen gases. Thin films were grown with different cobalt concentrations and analyzed by atomic force microscopy, spectrophotometry, X-ray photoelectron spectroscopy, X-ray reflectometry and vibrating sample magnetometry. We have found that the films readily oxidize after exposure to the atmosphere and form a cobalt doped titanium oxynitride. The variable cobalt concentration in the films affects the optical, chemical and magnetic properties. The bandgap of the films generally becomes narrower at higher cobalt concentrations. Cobalt is found to be in a mixture of the high spin + 2 and low spin + 3 oxidation states. At the lower cobalt concentrations, the magnetization is low and it is temperature-independent. Whereas at higher cobalt concentrations, the magnetic response becomes temperature-dependent with a mix of paramagnetism and superparamagnetism at 3–5 K.