Possible Existence of Dense Ferrimagnetic Perovskite Allotropic Form of Yttrium Iron Garnet

Mixed oxides with the same chemical composition as yttrium iron garnet (YIG) were maintained at 900°C and 20 kbars for 30 min. X-ray diffraction showed that the product was single-phase. Since the diffraction pattern could be indexed as a structure similar to yttrium ortho-ferrite, YFeO₃, the product was considered to be a deformed type of perovskite. Subsequently, the lattice constants were calculated to be a = 5.27, b = 5.57, and c = 7.59 A. Both measured and calculated densities were about 6% greater than those of YIG. This material, therefore, can be called a dense allotropic form of YIG. Ferrimagnetism was observed in this phase; the Curie temperature and the magnetic moment at room temperature were estimated to be 625° C and 63 emu/g, respectively. This dense form converted to YIG on heating at 900° C for 4 hr in air. The transformation of YIG to a dense form at high pressures is inconsistent with the results reported by Marezio et al. Some possible reasons for this discrepancy are discussed.