High-temperature ferromagnetism in Fe-doped InSb: First-principles insights into defect-driven magnetic interactions

Fe-doped InSb is an n-type ferromagnetic semiconductor with high Curie temperatures above 300 K, offering a promising platform for semiconductor spintronics. To elucidate the microscopic origin of ferromagnetism in heavily Fe-doped InSb, we systematically investigate Fe defect configurations, magnetic interactions, and electronic structures using first-principles calculations based on cluster expansion and the Korringa–Kohn–Rostoker (KKR) Green’s function method. Our cluster expansion analysis indicates that Fe atoms occupy In substitutional sites below an Fe concentration of 20%, whereas interstitial Fe defects emerge above 20% and coexist with substitutional ones. This change in the dominant defect configurations is consistent with the experimentally observed behavior of the lattice constant: Vegard’s law is followed below 20%, whereas a slight upward deviation appears above 20%. Exchange-coupling analyses reveal that the coexistence of substitutional and interstitial Fe defects yields robust ferromagnetic networks and enables Curie temperatures to exceed room temperature. In particular, nearest-neighbor octahedral–tetrahedral interstitial Fe pairs exhibit exceptionally strong ferromagnetic coupling, which is attributed to direct exchange driven by orbital hybridization. Overall, these results provide first-principles insights into the defect-driven magnetic interactions underlying high-temperature ferromagnetism in Fe-doped InSb and offer practical guidelines for the design of semiconductor spintronic materials.