Long-range magnetic ordering in Na2IrO3

Abstract

We report a combined experimental and theoretical investigation of the magnetic structure of the honeycomb lattice magnet Na2IrO3, a strong candidate for a realization of a gapless spin-liquid. Using resonant x-ray magnetic scattering at the Ir L3-edge, we find 3D long range antiferromagnetic order below TN =13.3 K. From the azimuthal dependence of the magnetic Bragg peak, the ordered moment is determined to be predominantly along the a-axis. Combining the experimental data with first principles calculations, we propose that the most likely spin structure is a novel "zig-zag" structure.

Tuning into the Kitaev spin liquid phase: A spin model on the honeycomb lattice with two types of Heisenberg exchange couplings

“…The zigzag AFM order was found in experiments for the iridates [6][7][8][9]. This zig-zag order phase in the phase diagram appears in the third quarter of Fig.…”

“…A phase transition from a stripy antiferromagnetic(AFM) order to the Kitaev SL phase was predicted. Experiments for the iridates, however, found a zig-zag AFM order [6][7][8][9]. These progresses drive a number of further researches [10][11][12][13][14][15][16][17][18].…”

IrSr2Sm1.15Ce0.85CuColman1, Mclaughlin2 2012Phys. Rev. B

“…13 This lattice effect is further evidenced from studies of Ru 1−x Ta x Sr 2 Nd 0.95 Y 0. 15 Ce 0.9 Cu 2 O 10 materials; MR 9T (4 K) increases from − 28% to − 49% as x increases from 0 to 0.2, which further expands the unit cell. 12 In an attempt to broaden this library of layered cuprates and search for further novel properties, we have experimented with the substitution of alternative transition metals into the 1222-layered structure.…”

Finite-temperature phase diagram of the classical Kitaev-Heisenberg model

“…Even so, the Kitaev spin liquid in honeycomb iridates has not been observed yet; in both Na 2 IrO 3 and Li 2 IrO 3 , magnetic order has been observed at low temperatures. [7][8][9] Moreover for Na 2 IrO 3 , the KH model in its original form does not appear to be sufficient to account for neither the zigzag magnetic order nor the spectrum of magnetic excitations that have been measured in neutron scattering experiments. 8,9,11 To explain the experimental observations in Na 2 IrO 3 , three different modifications of the super-exchange model have been proposed.…”

“…Recently, Jackeli and Khaliullin 1 suggested that the Kitaev model could actually be realized within the honeycomb iridates with general formula A 2 IrO 3 , since the anisotropic part of the interactions among Ir-ions has the same form as the Kitaev coupling. This suggestion has triggered a lot of experimental [7][8][9][10][11] and theoretical [12][13][14][15][16][17][18] activity in the study of Na 2 IrO 3 and Li 2 IrO 3 compounds.…”