Magneto-optical effect in anodized Al2O3 film with micropores electrodeposited with Co

Abstract

We have electrodeposited Co into the micropores of an anodic Al₂O₃ coating on Al, making Co rods of about 120 Å in diameter and 0.3–1 μm in length. The Al₂O₃ is amorphous, while the Co is crystalline (hexagonal form) with no preferred orientation exhibiting saturation magnetization 80% of that of bulk Co. The composite Al₂O₃/Co film shows prominent magnetic anisotropy perpendicular to the surface due to the shape anisotropy of the Co rods, having coercive force of ∼1.2 kOe. The Kerr rotation and the reflectivity of the films at λ=0.63 μm, Θ̂_k =±15’ to ±50’, and R=5 to 15% varied from sample to sample due to interference effect of light in the films. The values of θ_k and R change irreversibly when heated above ∼150 °C. Stripping the Al₂O₃‐Co film from the Al substrate by dissolving the Al, we have measured the Faraday effect and light transmittance. They increase linearly with increasing rod length, giving Θ̂_f(rotation) =−0.41 deg/μm, Ψ̂_f(ellipticity) =1.14 deg/μm, and α̂(absorption coefficient)=1.1 μm⁻¹. These values conform with what is expected from the effective dielectric tensor, including off‐diagonal elements, which we [Jpn. J. Appl. Phys. 2 3, 1580 (1984)] have formulated for composite materials containing magnetic fine particles or rods.