Fabrication, magnetism and high frequency application of exchange-coupled Fe 65Co 35±2–SiO 1.7±0.2 granular films

Abstract

A series of (Fe 65Co 35±2) x –(SiO 1.7±0.2) 1− x nano-granular films with various metal volume fractions ( x) were fabricated by rf sputtering. In a wide range, excellent soft magnetic properties have been achieved. In the x range from 0.7 to 0.48, the films exhibit small coercivity H c not exceeding 4 Oe and high electrical resistivity ρ up to 1.15 × 10 4 μΩ cm. And a minimum H c value of 1.65 Oe was obtained for the sample of x = 0.57 with ρ = 2.86 × 10 3 μΩ cm. At a frequency lower than 2.0 GHz, the real part μ′ of complex permeability of this sample is more than 170 and the FMR frequency is as high as 2.6 GHz, implying a high cut-off frequency for high frequency applications. With decreasing Fe 65Co 35±2 volume fraction, the resistivity of films increases remarkably and the grain size decreases obviously. At the same time, the coercivity H c decreases with grain size decreasing, which is consistent with the conclusion resulted from random anisotropy model quoted by Herzer. Study on Henkel plots shows that intergranular ferromagnetic exchange coupling exists among grains and is important for realizing soft magnetic properties.