Investigating magnetic anisotropy and the stability of J_eff =1/2 state in Sr₂IrO₄ thin films under orthorhombic distortion

We have investigated the complex interplay between orthorhombic distortion and magnetic anisotropy in Sr₂IrO₄ thin films. By inducing a pronounced orthorhombic distortion on Sr₂IrO₄ thin films due to Ca₃Ru₂O₇ substrates, we effectively control the uniaxial magnetic anisotropy. From x-ray magnetic circular dichroism (XMCD), we have observed divergent responses along the system’s magnetic easy and hard axes, thereby indicating the existence of magnetic anisotropy. The magnetic anisotropy energy estimated from the spin flop transition, observed when the magnetic field is parallel to the hard axis, well matches the value calculated from the single magnon peak energy measured using Raman spectroscopy. Notably, the observed anisotropy energy remains lower than the theoretical estimates, emphasizing the persistence of the J_eff =1/2 state. This conclusion is supported by negligible XMCD intensity ratios and the expectation value of the spin-orbit coupling determined from the branching ratio using x-ray absorption spectroscopy. Our findings highlight the proximity of Sr₂IrO₄ to the J_eff =1/2 state despite substantial biaxial distortion, enhancing our understanding of the interplay between magnetic anisotropy and strain in materials with emergent quantum phenomena.