Study on microstructure and soft magnetism of (Fe 65Co 35) x(SiO 2) 1−x nano-granular films with very high ferromagnetic resonance frequency

Abstract

A series of (Fe 65Co 35) x (SiO 2) (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 Fe 65Co 35 magnetic metal particles uniformly embedded in an insulating SiO 2 matrix. (Fe 65Co 35) x (SiO 2) (1− x ) films exhibit large magnetic anisotropy field H k and excellent soft magnetic properties in a wide x range from 0.80 to 0.52 with coercivity H c smaller than 18 Oe. A minimum H c 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 H k 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 (Fe 65Co 35) x (SiO 2) (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.