Study on microstructure and soft magnetism of (Fe65Co35)x(SiO2)1−x nano-granular films with very high ferromagnetic resonance frequency

A series of (Fe65Co35)x(SiO2)(1−x) nano-granular films with different volume fraction x are fabricated by magnetron co-sputtering technique. The structure, magnetic and high frequency properties are investigated systematically by using X-ray diffraction, transmission electronic microscopy, vibrating sample magnetometer, resistivity and complex permeability measurements. Study results indicate that the films consist of Fe65Co35 magnetic metal particles uniformly embedded in an insulating SiO2 matrix. (Fe65Co35)x(SiO2)(1−x) films exhibit large magnetic anisotropy field Hk and excellent soft magnetic properties in a wide x range from 0.80 to 0.52 with coercivity Hc smaller than 18 Oe. A minimum Hc value of 7.8 Oe is obtained for the sample with x=0.60 whose electrical resistivity ρ reaches 2220 μ Ω cm and the magnetic anisotropy field Hk is as high as 185 Oe. Especially, for the result of complex permeability measurement of the samples, very high ferromagnetic resonance (FMR) frequency is obtained. For the typical sample with x=0.60, the FMR frequency reaches 4.9 GHz, implying a very high cut-off frequency for high frequency applications, and the real part μ′ of its complex permeability exceeds 60 below 3.8 GHz while the imaginary part μ″ is very small until f>2.0 GHz. These good high frequency properties imply that (Fe65Co35)x(SiO2)(1−x) granular films are promising for applications in high frequency range. The good soft magnetic properties are ascribed to the exchange coupling among magnetic particles, which is discussed in this paper.