Nanotwin-Induced Ferrimagnetism in an Antiferromagnetic Cr₂O₃ Thin Film on the SrTiO₃ Substrate

Nanotwinned materials have recently attracted intense interest since they often exhibit excellent mechanical properties that are far superior to those of the corresponding single crystals. However, how nanotwinned structures affect the physical properties of functional materials remains almost unexplored. In this study, we demonstrate ferrimagnetism in a nanotwinned antiferromagnetic Cr₂O₃ thin film. The Cr₂O₃ thin film grown on the SrTiO₃ substrate comprises high-density nanotwins and exhibits an obvious room-temperature ferrimagnetic property, though the bulk Cr₂O₃ is intrinsically antiferromagnetic. Aberration-corrected transmission electron microscopy investigations reveal that the twin boundaries (TBs) of Cr₂O₃ are stoichiometric and have two types of atomic structures (i.e., denoted by type I and type II). First-principles calculations suggest that the type I TB exhibits an antiferromagnetic nature without a net magnetic moment, while the type II TB is ferrimagnetic and has a net magnetic moment of 3.0 μ_B/f.u. These findings suggest that nanotwins in functional materials can generate physical properties distinct from those of single crystals, thereby providing an efficient strategy for material design and performance control.