Reverse-Engineering Strain in Nanocrystallites by Tracking Trimerons

Although strain underpins the behavior of many transition-oxide-based magnetic nanomaterials, it is elusive to quantify. Since the formation of orbital molecules is sensitive to strain, a metal-insulator transition should be a window into nanocrystallite strain. Using three sizes of differently strained Fe₃ O₄ polycrystalline nanorods, the impact of strain on the Verwey transition and the associated formation and dissolution processes of quasiparticle trimerons is tracked. In 40 and 50 nm long nanorods, increasing isotropic strain results in Verwey transitions going from T_V ≈ 60 K to 20 K. By contrast, 700 nm long nanorods with uniaxial strain along the (110) direction have T_V ≈ 150 K-the highest value reported thus far. A metal-insulator transition, like T_V in Fe₃ O₄ , can be used to determine the effective strain within nanocrystallites, thus providing new insights into nanoparticle properties and nanomagnetism.