Biaxial strain effect induced electronic structure alternation and trimeron recombination in Fe₃O₄

The Verwey transition in Fe₃O₄ is the first metal-insulator transition caused by charge ordering. However, the physical mechanism and influence factors of Verwey transition are still debated. Herewith, the strain effects on the electronic structure of low-temperature phase (LTP) Fe₃O₄ with P2/c and Cc symmetries are investigated by first-principles calculations. LTP Fe₃O₄ with each space group has a critical strain. With P2/c, Fe₃O₄ is sensitive to the compressive strain, but it is sensitive to tensile strain for Cc. In the critical region, the band gap of LTP Fe₃O₄ with both two symmetries linearly increases with strain. When strain exceeds the critical value, DOS of spin-down t_2g electron at Fe(B4) with P2/c and Fe(B42) with Cc changes between d_x2_-y2 and d_xz + d_yz. The trimerons appear in Cc can be affected by strain. With a compressive strain, the correlation of trimeron along x and y axes is strengthened, but broken along the face diagonal of Fe_B4O₄, which is opposite at the tensile strains. The results suggest that the electronic structure of Fe₃O₄ is tunable by strain. The narrower or wider band gap implies a lower or higher transition temperature than its bulk without strains, which also gives a glimpse of the origin of charge-orbital ordering in Fe₃O₄.