Abstract

Pure and chromium substituted yttrium iron garnets Y₃Fe_{5 − x}Cr_xO₁₂ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) have been made in air using self-propagating high-temperature synthesis (SHS), a combustion process involving the reaction of yttrium(III) oxide, iron(III) oxide, chromium(III) oxide, iron metal powder and sodium perchlorate. 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 Mössbauer 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 sized 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.