Outstanding <i> T _C </i> Enhancement in 5 <i>d–</i> 3 <i>d</i> Y ₂ NiIrO ₆ by Compression

ABSTRACT Understanding and predicting the properties of 5 d compounds critically depend on the identification of the superexchange interactions from which their magnetism emerges. The study of pressure effects on double perovskite Y 2 NiIrO 6 (YNIO) provides deep insight toward this goal. At ambient pressure, YNIO is a ferrimagnetic insulator with the Ir 4+ ‐5 d J eff = 1/2 Mott‐insulating state. Under physical pressure up to 17 GPa, the compound exhibits concurrent compression on Ni/Ir─O bond lengths and Ni─O─Ir bond angles, leading to an increase of the Curie temperature from 192 to 243 K. On the contrary, external pressure increases distanced Ir─Ir interaction and in turn induces magnetic frustration in Sr 2 IrO 4 /Sr 3 Ir 2 O 7 due to the extended 5 d orbitals. In YNIO, the rock‐salt ordered Ni─Ir naturally blocks extended superexchange beyond the nearest neighbor, and in turn suppresses such magnetic frustration. Moreover, the orthogonal Ni e g –Ir t 2g pathway in YNIO is robust under lattice distortion, while the superexchange is weakened by bond bending in La 2 NiMnO 6 with a similar half‐filed e g – t 2g configuration. Our findings establish a framework for elucidating the mechanism of 5 d –3 d superexchange and guide bond‐engineered magnetism in iridate‐related systems.