Soft Magnetism and High Frequency Properties of Fe ₆₅ Co ₃₅ -MgF ₂ Granular Thin Films

Abstract

Fe65Co35)𝑥(MgF2)1−𝑥 films with different metal volume fraction 𝑥 are fabricated by magnetron sputtering. The results reveal that good soft magnetic properties can be obtained in a very wide 𝑥 range (0.9 > 𝑥 > 0.55) with 𝐻𝑐 not exceeding 10 Oe, and high resistivity is also realized for the samples. Especially for the sample with 𝑥 = 0.75, the coercivity in hard and easy axes is 1.6 Oe and 8.5 Oe, respectively, 4𝜋𝑀𝑠 = 14.1 kG and 𝜌 reaches 1.16 mΩ•cm. The dependence of complex permeability 𝜇 = 𝜇 ′ − 𝑗𝜇 ′′ on frequency shows that the real part 𝜇 ′ is more than 190 below 2.0 GHz and ferromagnetic resonance frequency 𝑓𝑟 reaches 2.43 GHz, implying that the film is promising for high frequency applications. High resolution transmission electron micrographs show that the films consists of bcc Fe65Co35 particles embedded uniformly in an amorphous insulating MgF2 matrix with particle size around a few nanometers. The excellent soft magnetic properties and high frequency properties are ascribed to exchange of coupling among magnetic granules, and the exchange coupling variation in a wide 𝑥 range (0.9 > 𝑥 > 0.55) is studied systematically by Δ𝑀 plots.