Magnetic and microwave properties of amorphous FeCoNbBCu thin films

The soft magnetic and microwave properties of amorphous FeCoNbBCu thin films with thicknesses varying from 70 nm to 450 nm have been systematically investigated. Due to the amorphous structure, the coercivity is 1.5 Oe in thicker films. The thickness-dependent microwave characteristics of the films were measured over the range 0.5–6 GHz and analyzed using the Landau–Lifshitz–Gilbert equation. Without applying magnetic field during deposition and measurement, an in-plane uniaxial anisotropy in amorphous thin films was obtained, ranging from 21 to 45 Oe. The interface interaction between substrate and film is confirmed to be the origin of the induced anisotropy, whereas the volume anisotropy contribution is more pronounced with increasing film thickness. For films possessing an in-plane uniaxial anisotropy, the shift of resonance frequency with thickness is observed and verified by the Kittel equation. The demonstration of a controllable and tunable anisotropy suggests that the FeCoNbBCu thin films have potential application as magnetic materials for Spintronics-based microwave devices.