Study on mechanism of soft magnetic properties for high-frequency application in Ni75Fe25-SiO2 granular films

Abstract

Excellent soft magnetic properties have been achieved in a wide metal volume fraction (x) range for as-deposited (Ni75Fe2.5)(x)-(SiO2)((1-x)) granular films fabricated by magnetron sputtering. With x changes from 0.81 to 0.52, the films exhibit small coercivity (H-c) not exceeding 5 Oe and high electrical resistivity p. The minimum H-c value of 87.6 A m(-1) was obtained for the sample of x = 0.81. At the frequency lower than 550 MHz, the real part mu' of complex permeability keeps about 170 and the image part mu" is less than 26. Especially, for the film with very low 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. A combined study of TEM and XRD indicates that the samples consist of Ni75Fe25 particles uniformly embedded in insulating SiO2 matrix. The excellent soft magnetic property is ascribed to the exchange coupling among magnetic particles due to the long exchange length of Ni75Fe25. The investigation of the Henkel plot evidences the existence of this intergranular interaction.