Magnetic properties of cobalt films at the initial stage of ion-beam deposition

Variations in the magnetic properties of ion-beam-deposited cobalt (Co) films from the onset of nucleation until the passage to a bulk-like state have been studied using ferromagnetic resonance (FMR) measurements at 9.55 GHz and SQUID magnetometry. Depending on the Co film thickness, the FMR line width Δ H exhibits a sharp transition from large values (0.24 kOe < Δ H < 0.33 kOe) at the initial deposition stage to slightly varying values of Δ H < 0.16 kOe for film thicknesses above 1 nm. Similarly, Co films with thicknesses below 1 nm exhibit a significant coercivity ( H C > 0.54 kOe at 10 K), while thicker films are characterized by H C < 0.16 kOe in the entire range of temperatures up to 300 K. Large values of Δ H and H C at the nucleation and initial growth stages are related to the contribution from a transition Co/Si layer formed under the action of self-irradiation with a high-energy component of the deposited flux, which is inherent in the ion-beam sputtering in high vacuum. This fraction of high-energy Co atoms does not exceed 10% of their total flux and is characterized by a mean projected range of 0.8 nm in the growing Co layer and 1.2 nm in the Si substrate. Conditions of using Co films with intermediate thicknesses within 0.8 nm < t ≤2 nm for the injection of a spin-polarized current into silicon at room temperature are discussed.