Exploring magnetic anisotropy and robustness of the J_eff = 1/2 state under substantial orthorhombic distortion in Sr₂IrO₄ thin films

Journal Article · 14 March 2024 · Physical Review. B

DOI: https://doi.org/10.1103/physrevb.109.104415 · OSTI ID:2326936

Shrestha, Sujan  ^[1]; Choi, Y. ^[2]; Krautloher, M. ^[3]; Zhu, M. ^[4]; Hwang, J. ^[4]; Keimer, B. ^[3]; Seo, Ambrose S.  ^[1]; Kim, J. -W. ^[2]

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1. Univ. of Kentucky, Lexington, KY (United States)
2. Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
3. Max Planck Institute of Solid State Research, Stuttgart (Germany)
4. The Ohio State Univ., Columbus, OH (United States)

Here, we present a comprehensive study revealing the intricate interplay of the magnetic anisotropy and orthorhombic distortion in thin films of Sr₂IrO₄ through a Ca₃Ru₂O₇ substrate. By inducing a pronounced orthorhombic distortion along the direction of oxygen octahedral edges, we effectively modulated the uniaxial magnetic anisotropy in the system. Remarkably divergent responses along the easy and hard magnetic axes were unveiled through x-ray magnetic circular dichroism (XMCD) measurements under magnetic fields. Specifically, the spin flop transition observed when the magnetic field aligns with the hard axis allows us to estimate the magnetic anisotropy energy, which is around 14.2 µeV, close to that estimated from the single magnon peak measured via Raman spectroscopy. The observed anisotropy energy remains notably lower than the linear estimates derived from the strain-anisotropy energy relationship outlined in H.-H. Kim et al., Nat. Commun. 13, 6674 (2022). This underscores the enduring preservation of the isotropic character of the J_eff = 1/2 states. This is also supported by the negligible XMCD intensity ratio at the L₂ edge compared to that of the L₃ edge. Furthermore, the branching ratio determined from x-ray absorption spectroscopy shows that the expectation value of the spin-orbit coupling is similar to that of bulk Sr₂IrO₄ single crystals. Our findings indicate that even under a substantial anisotropic biaxial distortion, Sr₂IrO₄ remains remarkably proximate to the J_eff = 1/2 state. This study not only provides valuable information in understanding the interplay between magnetic anisotropy and strain but also the robustness of the J_eff = 1/2 state under octahedral distortion within materials exhibiting emergent quantum phenomena.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); National Science Foundation (NSF); USDOE
• Grant/Contract Number: AC02-06CH11357; DMR-2104296; DMR-1847964
• OSTI ID: 2326936
• Alternate ID(s): OSTI ID: 2474526
• Journal Information: Physical Review. B, Vol. 109, Issue 10; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English