Fabrication and study of Ni75Fe25-SiO2 granular films for high frequency application

A series of (Ni₇₅Fe₂₅)_x(SiO₂)_(1-x) films with different volume fraction x is fabricated by magnetron co-sputtering technique. The structure, magnetic and high frequency properties are investigated systematically by X-ray diffraction, transmission electronic microscopy, vibrating sample magnetometer, resistivity and complex permeability measurements. The results show that the films consist of Ni₇₅Fe₂₅ magnetic metal particles uniformly embedded in the insulating SiO₂ matrix. The (Ni₇₅Fe₂₅)_x(SiO₂)_(1-x) films exhibit excellent soft magnetic properties in a wide x range from 0.81 to 0.52 with coercivity H_c not exceeding 5 Oe, which is ascribed to the exchange coupling between magnetic particles due to the long exchange length of Ni₇₅Fe₂₅ alloy. The smallest H_c is 1.1 Oe obtained for the sample of x=0.81 with high electrical resistivity ρ=167 μΩ·cm, and the real part μ´ of its initial complex permeability keeps constant of 170 below 550MHz while the imaginary part μ´´ is less than 26. The rapid increase of μ´´ at the frequency higher than 600MHz can be attributed to the ferromagnetic resonance, whose frequency is estimated to be about 2.2GHz. For the film of x= 0.52, besides the low H_c (∼3Oe), very high ρ over 1.18×10⁴ μΩ·cm has been obtained, implying that this film is quite promising for very high frequency application.