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Abstract Iron garnets that combine robust perpendicular magnetic anisotropy (PMA) with low Gilbert damping are desirable for studies of magnetization dynamics as well as spintronic device development. This paper reports the magnetic properties of low‐damping bismuth‐substituted iron garnet thin films (Bi_0.8Y_2.2Fe₅O₁₂) grown on a series of single‐crystal gallium garnet substrates. The anisotropy is dominated by magnetoelastic and growth‐induced contributions. Both stripe and triangular domains form during field cycling of PMA films, with triangular domains evident in films with higher PMA. Ferromagnetic resonance measurements show damping as low as 1.3 × 10⁻⁴with linewidths of 2.7 to 5.0 mT. The lower bound for the spin‐mixing conductance of BiYIG/Pt bilayers is similar to that of other iron garnet/Pt bilayers. 

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_0.36TbIG, and Bi_0.03TbIG films is 5400 ± 600° cm⁻¹, 4500 ± 100° cm^–1, and 6200 ± 300° cm⁻¹, respectively, while Ce_0.36TbIG and Bi_0.03TbIG 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 Bi_0.03TbIG of 720° dB⁻¹at 1550 nm, make these polycrystalline films valuable for applications in integrated photonics.