This study explores the low-temperature formation of yttrium iron garnet (YIG) and examines the structural and morphological changes induced by copper incorporation for potential terahertz applications. YIG precursors were synthesized via a conventional solid-state reaction and calcined at 600 °C. Copper oxide was subsequently introduced at 20 wt% and 30 wt% concentrations. The resulting Cu/YIG nanocomposites were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) surface area analysis to evaluate phase formation, grain size, surface characteristics, and porosity.

XRD analysis confirmed partial garnet phase formation at reduced temperature, with improved crystallinity and noticeable grain growth upon copper doping. FESEM images showed a morphological transition from porous, disconnected particles to more continuous and interconnected network structures with increasing Cu content. BET measurements revealed significantly increased specific surface area and enhanced porosity in the nanocomposite matrix.

These structural evolutions, driven by the presence of copper, suggest improved interconnectivity and conductive pathways in the resulting structure. Furthermore, the partial crystallinity retained at relatively low calcination temperatures highlights the feasibility of energy-efficient, low-cost processing routes. Taken together, these results demonstrate that the nanoporous semi-crystalline Cu/YIG composites are promising candidates for terahertz-frequency sensing due to their enhanced surface area, tunable microstructure, and potential for frequency-selective electromagnetic functionality.