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

Sheng-Chieh Huang¹, Kanchan Sarkar², Renata M. Wentzcovitch^3,4,5, Han Hsu^1*

¹Department of Physics, National Central University, Taoyuan City 32001, Taiwan
²Institute of Theoretical Chemistry, Ulm University, Ulm 89081, Germany
³Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA
⁴Department of Earth and Environmental Sciences, Columbia University, New York, New York 10027, USA
⁵Lamont–Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA

* Presenter:Han Hsu, email:hanhsu@ncu.edu.tw

At ambient pressure, bulk SrCoO₃ is a ferromagnetic (FM) metal in cubic perovskite structure. 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 a FM insulating state [2]. In this work, using first-principles calculations, we perform an extensive search for the structural, spin, magnetic, and orbital states of SrCoO₃ thin films. Our calculations indicate that at 0 < ε ≤ 2.5%, SrCoO₃ favors a FM half-metallic state with intermediate-spin (IS, t_2g⁵e_g¹-like) Co exhibiting d⁶L character. At ε ≥ 2.5%, a FM insulating state with high-spin (HS, t_2g⁴e_g²-like) Co dominates. This FM insulating state is achieved via complicated orbital ordering, cooperative Jahn–Teller distortion, and octahedral tilting about all three 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).

Keywords: SrCoO₃, orbital ordering, ferromagnetic insulator, epitaxial thin film, first-principles