Origin of Strong Ferromagnetic Couplings in Ordered Double Perovskite Semiconductors

Abstract

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 effective physical mechanism for strong FM couplings in semiconductors. Here, we focus on the double perovskite semiconductors to explore the mechanism of strong FM couplings. A remarkable correlation between magnetic couplings and spin occupation states in d orbitals has been revealed by a systematical comparison between the LaCrO 3 (LCO) and La 2 NiMnO 6 (LNMO) perovskites. First-principles calculations show that the LCO prefers an antiferromagnetic (AFM) ground state while the LNMO is FM. Such a disparity on magnetic coupling is mainly attributed to the difference on spin occupation states: the LCO has a d 3 -d 3 occupation state for each nearest-neighboring Cr-Cr pair, while the LNMO has a d 3 -d 8 occupation state for each Ni-Mn pair. The distinct different magnetic behaviors under strain and charge doping provide further evidence to the occupation-state-dependent magnetic coupling mechanism. Similar behavior has also been observed in other d <5 -d <5 and d <5 -d >5 , single-and doubleperovskites, 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.