Magnetic phase diagram of the frustrated S=1/2 triangular-lattice magnet Cu₂(NO₃)(OH)₃

Possible coexistence of short-range resonating-valence-bond and long-range stripe correlations in the spatially anisotropic triangular-lattice quantum magnet Cu$_2$(OH)$_3$NO$_3$

“…Our zero-field specific heat (C p ) measured on single-crystal samples also exhibits a broad peak at T N ∼ 8 K [Fig. 7(b)], but its absolute value (e.g., C p ∼ 9.4 JK −1 /mol-FU at 20 K) is only about one third of that previously reported on powder samples (C p ∼ 30 JK −1 /mol at 20 K) [40]. To figure this out, we also carefully measured the specific heat of the nondeuterated crystal (4.45 mg).…”

“…1), J 1a = −20 K and J 1b = 50 K, are stronger than all the others. As a result, the spin system of Cu 2 (OH) 3 NO 3 was expected to be composed of the independent ferromagnetic A and antiferromagnetic B chains in the recent work reported by Kikuchi et al [40], and the ordered moments of s z A ∼ 0.5 and s z B ∼ 0 were predicted at 0 T [40]. Our more strict many-body computation of the full model no.2 also points to a similar GS with more precise s z A ∼ 0.22 and s z B ∼ 0.00.…”

“…The spatially anisotropic triangular-lattice spin Hamiltonian with six NN Heisenberg exchange couplings was first estimated by Ruiz et al using density functional theory (DFT) and quantum Monte Carlo [39]. Recently, Kikuchi et al reported a longrange antiferromagnetic order at T N ∼ 8 K according to the thermodynamic and 1 H-NMR measurements on the powder sample [40]. However, such a magnetic order was not detected by powder neutron diffraction as previously reported by Drillon et al [38].…”

“…Furthermore, our DFT+U calculation suggests that the strength of second-neighbor (∼ 5.3 Å) intra-layer coupling J 2 is more than one order of magnitude smaller than those of the NN (∼ 3.1 Å) exchange couplings J 1 s. Therefore, we mainly restrict ourselves to the effective model with only NN Heisenberg exchange couplings for Cu 2 (OH) 3 NO 3 , as previously reported in Refs. [39,40].…”

“…Cu 2 (OH) 3 NO 3 (rouaite, space group P 2 1 ) is a structurally disorder-free triangular-lattice quantum (s =1/2) magnet that has been studied since a long time ago [37][38][39][40]. The spatially anisotropic triangular-lattice spin Hamiltonian with six NN Heisenberg exchange couplings was first estimated by Ruiz et al using density functional theory (DFT) and quantum Monte Carlo [39].…”