Fabrication and study of Ni/sub 75/Fe/sub 25/-SiO/sub 2/ granular films for high frequency application

Abstract

A series of (Ni/sub 75/Fe/sub 25/)/sub x/(SiO/sub 2/)/sub (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 Ni/sub 75/Fe/sub 25/ magnetic metal particles uniformly embedded in the insulating SiO/sub 2/ matrix. The (Ni/sub 75/Fe/sub 25/)/sub x/(SiO/sub 2/)/sub (1-x)/ films exhibit excellent soft magnetic properties in a wide x range from 0.81 to 0.52 with coercivity H/sub c/ not exceeding 5 Oe, which is ascribed to the exchange coupling between magnetic particles due to the long exchange length of Ni/sub 75/Fe/sub 25/ alloy. The smallest H/sub c/ is 1.1 Oe obtained for the sample of x=0.81 with high electrical resistivity /spl rho/=167 /spl mu//spl Omega//spl middot/cm, and the real part /spl mu/' of its initial complex permeability keeps constant of 170 below 550MHz while the imaginary part /spl mu/'' is less than 26. The rapid increase of /spl mu/'' 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/sub c/ (/spl sim/3Oe), very high /spl rho/ over 1.18/spl times/10/sup 4/ /spl mu//spl Omega//spl middot/cm has been obtained, implying that this film is quite promising for very high frequency application.