Outstanding T_C Enhancement in 5d-3d Y₂NiIrO₆ by Compression

Understanding and predicting the properties of 5d compounds critically depend on the identification of the superexchange interactions from which their magnetism emerges. The study of pressure effects on double perovskite Y₂NiIrO₆ (YNIO) provides deep insight toward this goal. At ambient pressure, YNIO is a ferrimagnetic insulator with the Ir⁴⁺-5d 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 Sr₂IrO₄/Sr₃Ir₂O₇ due to the extended 5d 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 La₂NiMnO₆ with a similar half-filed e_g-t_2g configuration. Our findings establish a framework for elucidating the mechanism of 5d-3d superexchange and guide bond-engineered magnetism in iridate-related systems.