Enhanced high-frequency electromagnetic properties of FeCoB-SiO2/SiO2 multilayered granular films

A series of FeCoB-SiO2/SiO2 multilayered granular films with various thickness were prepared by alternating co-sputtering FeCoB and SiO2 targets and single-sputtering SiO2 target. As-deposited films were annealed in a magnetic field at different temperature. The high-frequency magnetic and electrical transport properties were investigated. The films annealed above 250 °C show good soft magnetic properties and obvious uniaxial magnetic anisotropy. The resistivity (ρ), coercivity (Hce) decrease and complex permeability (μ-tilde), ferromagnetic resonance frequency (fr) increase with increasing annealing temperature and thickness. The desirable high ρ (∼5.92 mΩ cm), considerable frequency linewidth (Δf∼4.02 GHz) and high μ-tilde (μ′=120 at low frequency, μmax″=80) were obtained for the 252 nm films annealed at 250 °C. The amorphous or nanograin phase and strong exchange coupling effect are responsible for the good high-frequency magnetic performance. The electrical transport properties show the films with high ρ and large μ-tilde are near the conductive percolation threshold. Moreover, the Δf, damp coefficient (α) and Gilbert damping parameter (G) were discussed based on phenomenological Landau-Lifshitz-Gilbert equation.