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, Θ̂k =±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 θk 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 Θ̂f(rotation) =−0.41 deg/μm, Ψ̂f(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. 23, 1580 (1984)] have formulated for composite materials containing magnetic fine particles or rods.