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

Abstract

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 rho = 167 mu Omega(.)cm, and the real part mu' of its initial complex permeability keeps constant of 170 below 550 MHz while the imaginary part mu" is less than 26. The rapid increase of mu" at the frequency higher than 600 MHz can be attributed to the ferromagnetic resonance, whose frequency is estimated to be about 2.2 GHz. For the film of x = 0.52, besides the low H-c (similar to 3 Oe), very high rho over 1.18 x 10(4) mu Omega(.)cm has been obtained, implying that this film is quite promising for very high frequency application.