The magnetic motif and the wavefunction of Kramers ions in strontium iridate (Sr2IrO4)

Published data for strontium iridate at 10 K, obtained by means of resonant x-ray Bragg diffraction at iridium L edges (Kim et al 2009 Science 323 1329), imply a magnetic ordering wavevector (1, 1, 1) and iridium moments confined to the a-b plane. The latter feature is accommodated in an Ir 5d wavefunction that is a superposition of conjugate states in a Kramers doublet, in which the mixing angle is the orientation of the orbital angular momentum in the basal plane. Structure factors for magnetic reflections calculated as a function of the azimuthal angle are used to demonstrate a potential method for direct observation of the angle of orientation. The branching ratio for integrated 'white line' intensity is calculated from the known saturation magnetic moment, in the absence of Ir-O hybridization. Our findings do not support the principal claim of Kim et al of having observed the phase inherent to a partner of a Kramers doublet (J(eff) = 1/2) by means of resonant x-ray Bragg diffraction.