Large Room‐Temperature Exchange Bias in Y ₃ Fe ₅ O ₁₂ via Antiparallel Exchange Interaction with Magnetically Pinned CoFe ₂ O ₄ Nanoparticles

The rapid expansion of data‐driven technologies has intensified demand for energy‐efficient and secure information processing platforms. Insulator‐based spintronic devices, which leverage quantized spin waves (magnons), offer a promising solution. Among insulating materials, yttrium iron garnet (YIG; Y 3 Fe 5 O 12 ) is notable for its ultra‐low magnetic damping; however, its exchange bias (EB) effect at room temperature remains inadequate for robust device operation. In this study, a new materials platform is developed by pairing YIG with cobalt ferrite (CFO; CoFe 2 O 4 ), achieving a record‐high exchange bias field ( H EB ) of 59 ± 4 Oe at room temperature, as determined by angular‐dependent ferromagnetic resonance measurements of YIG–CFO bulk composites. This large H EB can be attributed to a strong antiparallel exchange interaction at the YIG–CFO interface. These findings indicate a promising route toward achieving strong EB effects in thin‐film YIG–CFO systems and provide a straightforward materials strategy for engineering enhanced magnetic coupling in insulating systems.