Microstructure and magnetism of FeCo-SiO₂ nano-granular films for high frequency application

Excellent soft magnetic properties have been achieved in a wide metal volume fraction (x) range for as-deposited (Fe₆₅Co₃₅) _x(SiO₂)_1-x granular films fabricated by magnetron sputtering. With the decrease in x from 0.7 to 0.5, the films exhibit small coercivity H_c not exceeding 4 Oe and high electrical resistivity ρ up to 5.48 × 10³ νΩ cm. A minimum H_c value of 1.7 Oe was obtained for the sample of x ≤ 0.57 with ρ ≤ 2.86 × 10³ νΩ cm. At a frequency lower than 1.3 GHz, the real part μ′ of complex permeability of this sample is about 170 and then decreases with frequency while the imaginary part μ″ is visible when f > 1 GHz, which may be caused by anisotropy dispersion. The FMR frequency is as high as 2.4 GHz, implying a high cut-off frequency for high frequency applications. A study of high resolution transmission electronic microscope indicates that the samples consist of Fe₆₅Co₃₅ particles uniformly embedded in an insulating SiO₂ matrix. The excellent soft magnetic property is ascribed to exchange coupling among magnetic particles. The investigation of the Δm-H curve evidences the existence of this inter-granule interaction.