Epitaxial Strain Effect On The J(Eff)=1/2 Moment Orientation In Sr2iro4 Thin Films

We have grown Sr2IrO4 (SIO) epitaxial thin films on SrTiO3 (STO) and NdGaO3 (NGO) substrates by a pulsed laser deposition method and characterized their structures and magnetic properties. We find that SIO films grown on STO substrates display tetragonal structure with a tensile strain of 0.13%, while SIO films grown on NGO substrates exhibit slightly orthorhombic structure with anisotropic biaxial tensile strains of 0.39% and 0.51% along the in-plane crystallographic axes. Although both films display insulating properties as bulk SIO does, their magnetic properties are distinct from that of bulk SIO. The ferromagnetic (FM) component of the J(eff) = 1/2 canted antiferromagnetic order, which emerges below similar to 240 K in bulk SIO, is significantly weakened in both films, with a greater weakening appearing in the SIO/NGO film. From structural and magnetoresistance anisotropy analyses for both films, we reveal that the weak FM component in SIO films is dependent on the epitaxial strain. The greater tensile strain leads to a smaller octahedral rotation: The rotation angle is similar to 9.7(1)degrees for the SIO/NGO film and similar to 10.7(2)degrees for the SIO/STO film. These findings indicate that the J(eff) = 1/2 moment orientation in SIO follows the IrO6 octahedral rotation due to strong spin-orbit interaction.