Cu₂IrO₃: A New Magnetically Frustrated Honeycomb Iridate

Abstract

We present the first copper iridium binary metal oxide with the chemical formula CuIrO. The material is synthesized from the parent compound NaIrO by a topotactic reaction where sodium is exchanged with copper under mild conditions. CuIrO has the same monoclinic space group (C2/c) as NaIrO with a layered honeycomb structure. The parent compound NaIrO is proposed to be relevant to the Kitaev spin liquid on the basis of having Ir with an effective spin of 1/2 on a honeycomb lattice. Remarkably, whereas NaIrO shows a long-range magnetic order at 15 K and fails to become a true spin liquid, CuIrO remains disordered until 2.7 K, at which point a short-range order develops. Rietveld analysis shows less distortions in the honeycomb structure of CuIrO with bond angles closer to 120° compared to NaIrO. Thus, the weak short-range magnetism combined with the nearly ideal honeycomb structure places CuIrO closer to a Kitaev spin liquid than its predecessors.

Thermodynamic Evidence of Proximity to a Kitaev Spin Liquid in Ag3LiIr2O6

“…The asymmetric broadening (Warren line shape) of the peaks between 18 and 24 • in the inset of Fig. 1e is commonly observed in the layered honeycomb structures [28][29][30]. It is analyzed in the Supplemental Fig.…”

Field-induced magnetic transition and spin fluctuations in the quantum spin-liquid candidate CsYbSe2

“…The spin interactions are restricted by the low-dimensional structure, which could enhance the spin fluctuations [2]. Until now most QSL candidates are proposed in the low-spin S=1/2 frustrated systems, such as A 2 IrO 3 (A=Na, Li, Cu), H 3 LiIr 2 O 6 , κ-(BEDT-TTF) 2 Cu 2 (CN) 3 , EtMe 3 Sb[Pd(dmit) 2 ] 2 , and RuCl 3 [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

Exotic Low-Energy Excitations Emergent in the Random Kitaev Magnet Cu2IrO3

“…Figure 1(c) shows the T −dependence of the static magnetic susceptibility χ dc (T ) of Cu 2 IrO 3 measured at µ 0 H = 1 T, together with the real component of ac susceptibility χ ac (T ). As T → 0 K, both χ dc (T ) and χ ac (T ) exhibit a steep increase without obvious saturation or kink, in spite of the large Curie-Weiss temperature Θ CW = −110 K [18]. It is remarkable that both χ dc (T ) and χ ac (T ) are described by a power-law increase χ(T ) ∼ T −αs with α s = 0.26 for temperatures below 20 K. Such a sub-Curie law behavior is indicative of the presence of abundant low-energy excitations.…”

“…As the real materials are vulnerable to a monoclinic stacking of honeycomb layers, non-Kitaev terms seem inevitable. A related issue is to engineer local crystal environments towards an optimal geometry to maximize the Kitaev interactions.Very recently, the new Kitaev honeycomb iridates H 3 LiIr 2 O 6 and Cu 2 IrO 3 have been derived from their ancestors A 2 IrO 3 through soft structural modifications [17,18]. H 3 LiIr 2 O 6 is obtained by replacing the interlayer Li + ions with H + from α-Li 2 IrO 3 , while the honeycomb layer remains intact.…”

“…Polycrystalline samples of Cu 2 IrO 3 were prepared by a topotactic reaction as described in Ref. [18]. Dc and ac magnetic susceptibilities were measured using a SQUID and a vibrating sample magnetometer (Quantum Design MPMS and VSM).…”