Spin and Orbital Contributions to Magnetically Ordered Moments in 5d Layered Perovskite Sr2IrO4

TL;DR

This study used non-resonant magnetic x-ray diffraction with a novel polarization technique to quantify the orbital and spin contributions to magnetic moments in Sr2IrO4, revealing a strong spin-orbit coupling effect.

Contribution

It introduces a new experimental method to accurately measure orbital and spin contributions in 5d transition metal oxides, providing insights into spin-orbit coupling effects.

Findings

The orbital-to-spin ratio <L>/<S> is approximately 5.0.

The ratio is slightly larger than the ideal J_eff=1/2 value of 4.

Results suggest orbital redistribution is not solely due to octahedral elongation.

Abstract

The ratio of orbital (L) and spin (S) contributions to the magnetically ordered moments of a 5d transition metal oxide, Sr2IrO4 was evaluated by non-resonant magnetic x-ray diffraction. We applied a new experimental setting to minimize the error in which we varied only the linear-polarization of incident x-ray at a fixed scattering angle. Strong polarization dependence of the intensity of magnetic diffraction was observed, from which we conclude that the ordered moments contain substantial contribution from the orbital degree of freedom with the ratio of <L>/<S> ~5.0, evidencing the pronounce effect of spin-orbit coupling. The obtained ratio is close to but slightly larger than the expected value for the ideal J_eff = 1/2 moment of a spin-orbital Mott insulator, |<J_1/2|L_z|J_1/2>|/|<J_1/2|S_z|J_1/2>| = 4, which cannot be accounted by the redistribution of orbital components within the t_2g bands associated with the elongation of the IrO6 octahedra.