Trans-scale spin Seebeck effect in nanostructured bulk composites based on magnetic insulator.

The spin Seebeck effect enables thermoelectric conversion through thermally generated spin currents in magnetic materials, offering a promising transverse geometry for scalable devices. However, conventional spin Seebeck devices are confined to nanoscale thin-film architectures, with significantly restricted output power due to the intrinsic constraints of spin and magnon diffusion lengths. Here, we demonstrate a trans-scale spin Seebeck effect using nanostructured bulk composites composed of Pt-coated yttrium iron garnet powders fabricated via dynamic powder sputtering and low-temperature sintering. The resulting three-dimensional composites exhibit continuous Pt channels and robust mechanical integrity. Transverse thermoelectric measurements reveal isotropic spin Seebeck signals at the bulk scale. Power analysis indicates that the three-dimensional architecture enables scalable volumetric thermoelectric power generation beyond diffusion-limited thin-film spin Seebeck geometries. This work establishes a scalable platform for spin Seebeck thermoelectric conversion, bridging nanoscale spin caloritronics with macroscopic device integration.