Magnetism and site occupancy in epitaxial Y-rich yttrium iron garnet films

Y-rich yttrium iron garnet (Y-YIG) thin films were grown on gadolinium gallium garnet substrates using pulsed laser deposition from a YFeO3 target. The films are epitaxial on the substrate, and the unit cell of (001)- and (111)-oriented Y-YIG undergoes a tetragonal or rhombohedral distortion, respectively. The Y-YIG has lower room temperature magnetization but higher low-temperature magnetization than bulk YIG, and its Curie temperature was in the range of 330-400 K, depending on the growth conditions. First-principles calculations predict that Y-Fe antisite defects are more stable in octahedral than tetrahedral Fe sites. Temperature-dependent magnetization measurements together with a superexchange dilution model and composition determined from x-ray photoelectron spectroscopy indicate that nonmagnetic species (Y3+ and vacancies) are predominantly accommodated in the octahedral sites, but there is a significant occupancy of tetrahedral sites.