Outstanding T _C Enhancement in 5 d– 3 d 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.