High Figure of Merit Magneto‐Optical Ce‐ and Bi‐Substituted Terbium Iron Garnet Films Integrated on Si

Abstract

Films of polycrystalline terbium iron garnet (TbIG), cerium-substituted TbIG (CeTbIG), and bismuth-substituted TbIG (BiTbIG) are grown on Si substrates by pulsed laser deposition. The films grow under tensile strain due to thermal mismatch with the Si substrate, resulting in a dominant magnetoelastic anisotropy which, combined with shape anisotropy, leads to in-plane magnetization. TbIG has a compensation temperature of 253 K which is reduced by substitution of Ce and Bi. The Faraday rotation at 1550 nm of the TbIG, Ce0.36TbIG, and Bi0.03TbIG films is 5400 ± 600° cm−1, 4500 ± 100° cm–1, and 6200 ± 300° cm−1, respectively, while Ce0.36TbIG and Bi0.03TbIG exhibit lower optical absorption than TbIG, attributed to a reduction in Fe2+ and Tb4+ absorption pathways. The high Faraday rotation of the films, and in particular the high magneto-optical figure of merit of the Bi0.03TbIG of 720° dB−1 at 1550 nm, make these polycrystalline films valuable for applications in integrated photonics.