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

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 degrees cm(-1), 4500 +/- 100 degrees cm(-1), and 6200 +/- 300 degrees cm(-1), respectively, while Ce(0.36)TbIG and Bi(0.03)TbIG 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 Bi(0.03)TbIG of 720 degrees dB(-1) at 1550 nm, make these polycrystalline films valuable for applications in integrated photonics.