Effect of Rare-Earth and Iron Sites Substitution on the Magneto-Optical Properties of Bi-Substituted Iron Garnets for Magnetic Holographic Memory

We have developed magnetic holographic recording media for magnetic holographic memory using transparent bismuth-substituted rare-earth iron garnets. To achieve bright and stable hologram reconstruction, a large residual Faraday rotation angle and a moderately low extinction coefficient are required. In this study, Bi, Dy and Al-substituted yttrium iron garnet, (Bi,Dy,Al):YIG, thin films were prepared by the metal–organic decomposition method and systematically characterized. X-ray diffraction indicated the formation of garnet structures with no detectable secondary crystalline phases. The lattice constant decreased with increasing Al content and increased with increasing Bi content, while Dy substitution showed no clear systematic effect on lattice parameters. Magneto-optical measurements showed that the saturated Faraday rotation angle increased with Bi substitution and decreased with increasing Al content. In high-Bi compositions, it also decreased with increasing Dy content. Faraday-loop measurements showed that Dy substitution increased the coercive field and improved the squareness ratio. This resulted in an enhanced residual Faraday rotation angle for films with higher Bi and Dy contents. Optical measurements showed a sharp absorption edge near 500 nm and high transmittance (80–90%) in the near-infrared region for all compositions. The extinction coefficient at 532 nm decreased with increasing Al substitution and exhibited weaker dependence on Dy content. Evaluation of the figure of merit, based on residual Faraday rotation angle and extinction coefficient at 532 nm, identified the composition x = 1.0, y = 1.4, and z = 1.0 as optimal, showing improved performance compared with the reference Bi:RIG.