Orbital-ordered ferromagnetic insulating state in tensile-strained SrCoO₃ thin films

At ambient pressure, bulk SrCoO₃ (cubic perovskite) is a ferromagnetic (FM) metal. By contrast, magnetic properties of epitaxial SrCoO₃ thin films, especially at high tensile strain (ε ≥ 3%), remain unclear: Previous calculations had predicted antiferromagnetic (AFM) states more energetically favorable in this regime [1], but recent experiments suggested an FM insulating state [2]. In this work, using first-principles calculations, we perform extensive search for the structural, spin, magnetic, and orbital states of SrCoO₃ thin films. Our calculations indicate that for 0 < ε ≤ 2.5%, SrCoO₃ thin films favor an FM half-metallic state with intermediate-spin (IS, t_2g⁵e_g¹-like) Co exhibiting d⁶L character (Co³⁺ accompanied by O 2p holes). For ε ≥ 2.5%, an FM insulating state with high-spin (HS, t_2g⁴e_g²-like) Co prevails. This FM insulating state is achieved via complicated orbital ordering, cooperative Jahn–Teller distortion, and octahedral tilting about all crystal axes.

[1] J. H. Lee and K. M. Rabe, Phys. Rev. Lett. 107, 067601 (2011).

[2] Y. Wang et al., Phys. Rev. X, 10, 021030 (2020).