Dramatic enhancement of the saturation magnetization of a sol-gel synthesized Y₃Fe₅O₁₂ by a mechanical pressing process

We fabricated polycrystalline yttrium-iron-garnet (Y₃Fe₅O₁₂, YIG) samples using the sol-gel synthesis method to develop an energy harvesting material based on the spin Seebeck effect. We confirmed that crystallization occurred during calcination at 850 °C and that only the polycrystalline YIG structure was formed. We found that a sintering process at 1400 °C not only increased the size of the YIG particles and the densification of their microstructure but also enhanced their saturation magnetization (M_s) and dramatically reduced their coercivity (H_c). A mechanical pressing process was carried out between the calcination and sintering treatments to prepare a free-standing YIG fillet sample. We found that M_s was enhanced by almost three times without an associated reduction in H_c. We found that mechanical pressing assists the oxidation reaction during the subsequent sintering process by increasing the surface energy and densification before the heat treatment.