Self-propagating high temperature synthesis of yttrium iron chromium garnets Y3Fe5 − xCrxO12 (0 ≤ x ≤ 0.6)

Pure and chromium-substituted yttrium iron garnets, Y3Fe5- xCrxO12 (x = 0-0.6) were made in air using self-propagating high-temperature synthesis (SHS), a combustion process involving the reaction of Y2O3, Fe2O3, Cr2O3, Fe powder and NaClO4. Two series of samples were produced: Series 1, SHS followed by annealing at 1450 C for 4 h, and series 2, SHS in a magnetic field of 1.1 T followed by annealing at 1450 C for 4 h. SEM, EDAX, electron microprobe and IR measurements were carried out on both series of samples. X- ray data showed that in all cases nearly single-phase garnets were produced. Room temperature Mossbauer data showed that the Cr exclusively substituted for Fe on the octahedral site sublattice. Magnetic hysteresis data showed that the series 2 samples had consistently larger magnetisations and smaller coercivities than the corresponding series 1 samples. This was attributed to microstructural effects, including a tendency to form larger crystallites in the presence of an applied field. The magnetic data also indicated a maximum in magnetisation and minimum in coercivity for both series 1 and series 2 samples with a Cr content of x = 0.3, the origins of which are discussed. 30 refs.