Investigation into the microstructure and soft magnetic property of co-sputtering FeNi–MgO nanogranular films

Abstract

A series of FeNi–MgO nanogranular soft magnetic films with different sputtering powers of MgO were deposited by co-sputtering at room temperature on naturally oxidized silicon substrates. By adjusting the sputtering power of MgO, the average grain size of FeNi–MgO granular film reduces from 6.5 to 4 nm. The easy-axis coercivity Hce decreases from 8 to 0.3 Oe and saturation field Hs decreases from 14 to 1 Oe. When the sputtering power of MgO is above 60 W, Hce and Hs keep nearly unchanged. The results of permeability spectra indicate that the resonant frequency fr can be modulated in a small range from 0.61 to 0.71 GHz. Meanwhile, Gilbert damping α first decreases and then increases with increasing the sputtering power of MgO. The initial permeability is higher than 500 when the frequency is below 0.5 GHz, indicating that the FeNi–MgO nanogranular films are the excellent candidate for a high-frequency application.