Fabrication and magnetism of Fe65Co35-MgF2 granular films for high frequency application

A series of (Fe65Co35)x(MgF2)1−x films with different metal volume fraction x was fabricated by magnetron sputtering. High resolution transmission electron micrographs show that the film consists of bcc Fe65Co35 particles uniformly embedded in an amorphous insulating MgF2 matrix with particle size around a few nanometers. The research results reveal that high sputtering power (200 W) leads to the occurrence of FeCo fluorides, which are harmful to soft magnetic properties. For the samples fabricated using 60 W, good soft magnetic properties have been obtained in a wide x range (x=0.9−0.55), with Hc not exceeding 10 Oe, along with high resistivity. In particular, for the sample with x=0.62, coercivities in hard and easy axes are 0.6 and 7.2 Oe, respectively, 4πMs=11.5 kG, and ρ reaches 2.53 mΩ cm. The dependence of complex permeability μ=μ′−jμ″ on frequency shows that the real part μ′ is more than 100 below 1.0 GHz and ferromagnetic resonance frequency reaches 2.35 GHz. The excellent soft magnetic property is ascribed to the exchange coupling among magnetic granules.