Fabrication, magnetism and high frequency application of exchange-coupled Fe65Co35±2-SiO1.7±0.2 granular films

A series of (Fe65Co35±2)x-(SiO1.7±0.2)1−x nano-granular films with various metal volume fractions (x) were fabricated by rf sputtering. In a wide range, excellent soft magnetic properties have been achieved. In the x range from 0.7 to 0.48, the films exhibit small coercivity Hc not exceeding 4 Oe and high electrical resistivity ρ up to 1.15 × 104 μΩ cm. And a minimum Hc value of 1.65 Oe was obtained for the sample of x = 0.57 with ρ = 2.86 × 103 μΩ cm. At a frequency lower than 2.0 GHz, the real part μ′ of complex permeability of this sample is more than 170 and the FMR frequency is as high as 2.6 GHz, implying a high cut-off frequency for high frequency applications. With decreasing Fe65Co35±2 volume fraction, the resistivity of films increases remarkably and the grain size decreases obviously. At the same time, the coercivity Hc decreases with grain size decreasing, which is consistent with the conclusion resulted from random anisotropy model quoted by Herzer. Study on Henkel plots shows that intergranular ferromagnetic exchange coupling exists among grains and is important for realizing soft magnetic properties.