| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 5366530 | Applied Surface Science | 2012 | 7 Pages |
The microstructure evolution in several polycrystalline yttrium iron garnet samples as a result of a sintering scheme was studied in detail, in parallel with the changes in their magnetic properties. Samples with nanometer sized starting powder were synthesized by employing the High-Energy Ball Milling technique and then sintering toroidal compacts of the milled powder. Nine sintered samples were obtained, each corresponding to a particular sintering from 600 °C to 1400 °C. The samples were characterized for their evolution in crystalline phases, microstructure and magnetic hysteresis-loops parameters. The results showed an increasing tendency of the saturation magnetization and saturation induction with grain size, which is attributed to crystallinity increase and to reduction of demagnetizing fields in the grains. The variation in coercivity could be related to anisotropy field changes within the samples due to grain size changes. In particular, the starting appearance of room temperature ferromagnetic order suggested by the sigmoid-shaped B-H loops seems to be dependent on a sufficient number of large enough magnetic domain-containing grains having been formed in the microstructure. Viewed simultaneously, the hysteresis loops appear to belong to three groups with different magnetism-type dominance, respectively dependent on phase purity and three different groups of grain size distributions.
⺠Parallel evolutions of morphological and magnetic properties and their relationships at various sintering temperatures. ⺠A complete phase of Yttrium Iron Garnet was formed at sintering temperature lower than that in the conventional technique. ⺠3 hysteresis loop groups evolved indicating three evolution stages: weak, moderate and strong ferromagnetism. ⺠Phase purity, crystallinity and microstructural effect clearly described the evolution of these 3 groups of hysteresis loops. ⺠Crystallinity could be estimated from Bs and Ms value; magnetization process could be identified from Hc value at particular grain size.
