Interfacial and Bulk Magnetic Properties of Stoichiometric Cerium Doped Terbium Iron Garnet Polycrystalline Thin Films

One of the best magneto‐optical claddings for optical isolators in photonic integrated circuits is sputter deposited cerium‐doped terbium iron garnet (Ce:TbIG) which has a large Faraday rotation (≈−3500° cm−1 at 1550 nm). Near‐ideal stoichiometry Ce + TbFe = 0.57 of Ce0.5Tb2.5Fe4.75O12 is found to have a 44 nm magnetic dead layer that can impede the interaction of propagating modes with garnet claddings. The effective anisotropy of Ce:TbIG on Si is also important, but calculations using bulk thermal mismatch overestimate the effective anisotropy. Here, X‐ray diffraction measurements yield highly accurate measurements of strain that show anisotropy favors an in‐plane magnetization in agreement with the positive magnetostriction of Ce:TbIG. Upon doping TbIG with Ce, a slight decrease in compensation temperature occurs which points to preferential rare‐earth occupation in dodecahedral sites and an absence of cation redistribution between different lattice sites. The high Faraday rotation, large remanent ratio, large coercivity, and preferential in‐plane magnetization enable Ce:TbIG to be an in‐plane latched garnet, immune to stray fields with magnetization collinear to direction of light propagation. High‐gyrotropy garnet on silicon is obtained despite the presence of a magnetic dead layer at the substrate thin‐film interface. A near‐ideal stoichiometry and compensation temperature in sputter‐deposited cerium‐doped terbium iron garnet (Ce:TbIG) suggests a lack of cation redistribution. A low room‐temperature magnetization, high coercivity, large remnant magnetization, and anisotropy‐ aided preferential in‐plane magnetization are beneficial for magnetless non‐reciprocal mode conversion optical isolators.