High-frequency FeCoNiNbB–SiO2 nano-granular films with high resistivity and adjustable resonance frequency from 1.3 to 7.8 GHz

A series of (FeCoNiNbB) x –(SiO 2 ) 1− x nano-granular thin films were fabricated by magnetron sputtering with different oblique incidence angles θ . High-resolution transmission electron micrographs show that the films consist of amorphous CoFeM (M = Ni, Nb, B) alloy particles with diameter about 2 nm surrounded by amorphous SiO 2 matrix. Excellent soft magnetic properties have been achieved with a variable in-plane uniaxial magnetic anisotropy field H k 0 , which increases monotonically with θ and x , and decreases with the composition of B in FeCoM. For one typical sample of x =0.63 with θ =30°, H ch and H ce are 4.2 Oe and 5.4 Oe, respectively, ρ reaches 12.5 mΩ cm and 4 π M s and H k 0 are 5.70 kG s and 92 Oe, respectively, which lead to a high ferromagnetic resonance frequency f r of 2.2 GHz. Based on the analysis of experimental results, two sources for the origin of the magnetic anisotropy, namely anisotropic magnetic coupling and orientation order of atomic pairs, are suggested.