Critical fluctuations in the spin-orbit Mott insulator Sr3Ir2O7.

X-ray magnetic critical scattering measurements and specific heat measurements were performed on the perovskite iridate [Formula: see text]. We find that the magnetic interactions close to the Néel temperature [Formula: see text] are three-dimensional. This contrasts with previous studies which suggest two-dimensional behaviour like Sr2IrO4. Violation of the Harris criterion ([Formula: see text]) means that weak disorder becomes relevant. This leads a rounding of the antiferromagnetic phase transition at [Formula: see text], and modifies the critical exponents relative to the clean system. Specifically, we determine that the critical behaviour of [Formula: see text] is representative of the diluted 3D Ising universality class.

Resonant x-ray scattering and the j(eff) = 1/2 electronic ground state in iridate perovskites.

The resonant x-ray scattering (magnetic elastic, RXMS, and inelastic, RIXS) of Ir4+ at the L2,3 edges relevant to spin-orbit Mott insulators A(n+1)Ir(n)O(3n+1) (A = Sr, Ba, etc.) are calculated using a single-ion model which treats the spin-orbit and tetragonal crystal-field terms on an equal footing. Both RXMS and RIXS in the spin-flip channel are found to display a nontrivial dependence on the direction of the magnetic moment, µ. Crucially, we show that for µ in the ab plane, RXMS in the cross-polarized channel at the L2 edge is zero irrespective of the tetragonal crystal field; spin-flip RIXS, relevant to measurements of magnons, behaves reciprocally, being zero at L2 when µ is perpendicular to the ab plane. Our results have important implications for the assignment of a j(eff) = 1/2 ground state on the basis of resonant x-ray experiments.

Locking of iridium magnetic moments to the correlated rotation of oxygen octahedra in Sr2IrO4 revealed by x-ray resonant scattering.

Sr2IrO4 is a prototype of the class of Mott insulators in the strong spin-orbit interaction (SOI) limit described by a Jeff = 1/2 ground state. In Sr2IrO4, the strong SOI is predicted to manifest itself in the locking of the canting of the magnetic moments to the correlated rotation by 11.8(1)° of the oxygen octahedra that characterizes its distorted layered perovskite structure. Using x-ray resonant scattering at the Ir L3 edge we have measured accurately the intensities of Bragg peaks arising from different components of the magnetic structure. From a careful comparison of integrated intensities of peaks due to basal-plane antiferromagnetism, with those due to b-axis ferromagnetism, we deduce a canting of the magnetic moments of 12.2(8)°. We thus confirm that in Sr2IrO4 the magnetic moments rigidly follow the rotation of the oxygen octahedra, indicating that, even in the presence of significant non-cubic structural distortions, it is a close realization of the Jeff = 1/2 state.

Robustness of basal-plane antiferromagnetic order and the J(eff)=1/2 state in single-layer iridate spin-orbit Mott insulators.

The magnetic structure and electronic ground state of the layered perovskite Ba(2)IrO(4) have been investigated using x-ray resonant magnetic scattering. Our results are compared with those for Sr(2)IrO(4), for which we provide supplementary data on its magnetic structure. We find that the dominant, long-range antiferromagnetic order is remarkably similar in the two compounds and that the electronic ground state in Ba(2)IrO(4), deduced from an investigation of the x-ray resonant magnetic scattering L(3)/L(2) intensity ratio, is consistent with a J(eff)=1/2 description. The robustness of these two key electronic properties to the considerable structural differences between the Ba and Sr analogues is discussed in terms of the enhanced role of the spin-orbit interaction in 5d transition metal oxides.

The Jeff = 1/2 insulator Sr3Ir2O7 studied by means of angle-resolved photoemission spectroscopy.

The low-energy electronic structure of the J(eff) = 1/2 spin-orbit insulator Sr3Ir2O7 has been studied by means of angle-resolved photoemission spectroscopy. A comparison of the results for bilayer Sr3Ir2O7 with available literature data for the related single-layer compound Sr2IrO4 reveals qualitative similarities and similar J(eff) = 1/2 bandwidths for the two materials, but also pronounced differences in the distribution of the spectral weight. In particular, photoemission from J(eff) = 1/2 the states appears to be suppressed. Yet, it is found that the Sr3Ir2O7 data are in overall better agreement with band-structure calculations than the data for Sr2IrO4.

On the magnetic structure of Sr3Ir2O7: an x-ray resonant scattering study.

This report presents azimuthal dependent and polarization dependent x-ray resonant magnetic scattering at the Ir L(3) edge for the bilayered iridate compound Sr(3)Ir(2)O(7). The two magnetic wave vectors, k1 = (1/2, 1/2, 0) and k2 = (1/2, -1/2, 0), result in domains of two symmetry-related G-type antiferromagnetic structures, denoted A and B, respectively. These domains are approximately 0.02 mm(2) and are independent of the thermal history. An understanding of this key aspect of the magnetism is necessary for an overall picture of the magnetic behaviour in this compound. The azimuthal and polarization dependence of the magnetic reflections, relating to both magnetic wavevectors, show that the Ir magnetic moments in the bilayer compound are oriented along the c axis. This contrasts with single layer Sr(2)IrO(4) where the moments are confined to the ab plane.