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, Ce 0.36 TbIG, and Bi 0.03 TbIG films is 5400 ± 600° cm −1 , 4500 ± 100° cm –1 , and 6200 ± 300° cm −1 , respectively, while Ce 0.36 TbIG and Bi 0.03 TbIG exhibit lower optical absorption than TbIG, attributed to a reduction in Fe 2+ and Tb 4+ absorption pathways. The high Faraday rotation of the films, and in particular the high magneto‐optical figure of merit of the Bi 0.03 TbIG of 720° dB −1 at 1550 nm, make these polycrystalline films valuable for applications in integrated photonics.