Influence of sputtering power on the high frequency properties of nanogranular FeCoHfO thin films

Soft magnetic nanogranular FeCoHfO thin films were fabricated using rf magnetron sputtering in an oxygen/argon ambient. During the deposition process, the partial pressure of oxygen was fixed at 2.5% and sputtering power was used as the control parameter, varying from 50 to 300 W. It was found that the film electrical resistivity (ρ) decreases steeply with the increase of sputtering power, and the saturation magnetization (4πMs) and the natural ferromagnetic resonant frequency fr increase with increasing sputtering power from 50 to 200 W, and then decrease when sputtering power exceeded 200 W. The maximum value of 4πMs and fr were 20.5 kG and 3.2GHz, respectively. The coercivity of films had a contrary trend compared with 4πMs and fr, and its minimum value was about 1 Oe. The physical origin of the influence was suggested to be related to the structure and composition changes in films.