Origin of strong ferromagnetic couplings in ordered double perovskite semiconductors

Ferromagnetic (FM) semiconductors are crucial for advancing the development of spintronic devices for high-performance computing and data storage. However, to date, the realization of room-temperature FM semiconductors remains a great challenge owing to the lack of an effective physical mechanism for strong FM couplings in semiconductors. Herein, we focus on double perovskite semiconductors to explore the mechanism of strong FM couplings. A remarkable correlation between magnetic couplings and spin occupation states in d orbitals is revealed by a systematic comparison between LaCrO₃ (LCO) and La₂NiMnO₆ (LNMO) perovskites. First-principles calculations show that LCO prefers an antiferromagnetic (AFM) ground state, while LNMO is FM. Such a disparity in magnetic coupling is mainly attributed to the difference in spin occupation states: LCO has a d³–d³ occupation state for each nearest-neighboring Cr–Cr pair, while LNMO has a d³–d⁸ occupation state for each Ni–Mn pair. The distinctly different magnetic behaviors under strain and charge doping provide further evidence for the occupation-state-dependent magnetic coupling mechanism. Similar behavior has been observed in other d^<5–d^<5 and d^<5–d^≥5, single- and double-perovskites, demonstrating the generality of this mechanism. These findings unveil a novel mechanism and a strategy for realizing high-temperature FM semiconductors, which will significantly promote the development of spintronics.