Effect of isoelectronic doping on honeycomb lattice iridate A_2IrO_3

(2013)

Authors:

S Manni, Sungkyun Choi, II Mazin, R Coldea, Michaela Altmeyer, Harald O Jeschke, Roser Valenti, P Gegenwart

Effect of isoelectronic doping on honeycomb lattice iridate A_2IrO_3

ArXiv 1312.0815 (2013)

Authors:

S Manni, Sungkyun Choi, II Mazin, R Coldea, Michaela Altmeyer, Harald O Jeschke, Roser Valenti, P Gegenwart

Abstract:

We have investigated experimentally and theoretically the series (Na$_{1-x}$Li$_{x}$)$_{2}$IrO$_{3}$. Contrary to what has been believed so far, only for $x\leq0.25$ the system forms uniform solid solutions. For larger Li content, as evidenced by powder X-ray diffraction, scanning electron microscopy and density functional theory calculations, the system shows a miscibility gap and a phase separation into an ordered Na$_{3}$LiIr$_2$O$_{6}$ phase with alternating Na$_3$ and LiIr$_2$O$_6$ planes, and a Li-rich phase close to pure Li$_{2}$IrO$_{3}$. For $x\leq 0.25$ we observe (1) an increase of $c/a$ with Li doping up to $x=0.25$, despite the fact that $c/a$ in pure Li$_{2}$IrO$_{3}$ is smaller than in Na$_{2}$IrO$_{3}$, and (2) a gradual reduction of the antiferromagnetic ordering temperature $T_{N}$ and ordered moment. The previously proposed magnetic quantum phase transition at $x\approx 0.7$ may occur in a multiphase region and its nature needs to be re-evaluated.

Spin waves and revised crystal structure of honeycomb iridate Na2IrO3

Physical Review Letters 108 (2012) 127204

Authors:

SK Choi, R Coldea, AN Kolmogorov, T Lancaster, II Mazin, SJ Blundell, PG Radaelli, Y Singh, P Gegenwart, KR Choi, S-W Cheong, PJ Baker, C Stock, J Taylor

Abstract:

We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model on the honeycomb lattice. We observe spin-wave excitations below 5 meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zig-zag magnetic order. The onset of long-range magnetic order below 15.3 K is confirmed via the observation of oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we propose a revised crystal structure model with significant departures from the ideal 90 deg Ir-O-Ir bonds required for dominant Kitaev exchange.

Nature of the low energy excitations in the short range ordered region of Cs$_2$CuCl$_4$ as revealed by $^{133}$Cs NMR

(2012)

Authors:

M-A Vachon, G Koutroulakis, VF Mitrović, Ookie Ma, JB Marston, AP Reyes, P Kuhns, R Coldea, Z Tylczynski

Spin waves and revised crystal structure of honeycomb iridate Na2IrO3

(2012)

Authors:

SK Choi, R Coldea, AN Kolmogorov, T Lancaster, II Mazin, SJ Blundell, PG Radaelli, Yogesh Singh, P Gegenwart, KR Choi, S-W Cheong, PJ Baker, C Stock, J Taylor