Quantum phase transition in(CuCl)La(Nb1−xTax

Abstract

We demonstrate the synthesis and magnetic properties of a quasi-two-dimensional frustrated quantum spin system ͑CuCl͒La͑Nb 1−x Ta x ͒ 2 O 7 . We observed persistence of the spin-singlet state in ͑CuCl͒LaNb 2 O 7 up to x ϳ 0.4, accompanied by a slight reduction in the spin gap with increasing x. In spite of unaltered cell parameters and a preserved CuCl plane, ͑CuCl͒LaTa 2 O 7 exhibits collinear antiferromagnetic ͑CAF͒ order with T N ϳ 7 K as observed in ͑CuBr͒LaNb 2 O 7 . In the intermediate region ͑0.4Ͻ x Ͻ 1͒, we observed CAF order with a significantly reduced magnetic moment but with a nearly constant T N , suggesting that the CAF state coexists with the spin-singlet state in agreement with recent SR results.

Muon spin relaxation studies of the frustrated quasi-two-dimensional square-lattice spin systemCu(Cl,Br)La(Nb,TaUemura1, Aczel2, Ajiro3 et al. 2009Phys. Rev. BSelf Cite292150View full textAdd to dashboardCite

“…19,20 . X-ray diffraction results show no trace of impurity phases for the entire concentration regions 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1 within the experimental detection limit.…”

“…Since then a few parallel efforts have been made in neutron scattering, high-field susceptibility / magnetization, NMR, and Raman scattering measurements. While NMR and Raman studies have been / will be reported in separate independent papers 17,18 µSR and the remaining studies and characterization of the specimens will be reported in three consecutive papers (I, II 20 and III 19 ). In this paper (I), we focus on µSR and low-field magnetic susceptibility measurements on Cu(Cl,Br)La(Nb,Ta) 2 O 7 , which demonstrate: (a) absence of static magnetism in (CuCl)LaNb 2 O 7 down to 15 mK confirming the spin-gapped ground state; (b) phase separation between partial volumes with a spin-gap and static magnetism in (CuCl)La(Nb,Ta) 2 O 7 ; (c) historydependent magnetization in the (Nb,Ta) and (Cl,Br) substitution systems; and (d) a uniform long-range collinear antiferromagnetic state in (CuBr)LaNb 2 O 7 .…”

Ion-Exchange Reactions for Two-Dimensional Quantum Antiferromagnetism

“…Contrasting behaviors are observed in the Nb-site substituted system, (CuCl)La(Nb1-yTay)2O7 (0 y 1) [40]. Reflecting similar ionic radii between Nb 5+ and Ta 5+ , the lattice parameters are almost constant with y.…”

“…Two kinds of solid solutions have been investigated, against Br-for-Cl [38,39] and Ta-forNb [39,40] substitution. For (CuCl1  xBrx)LaNb2O7 (0 x 1), the a-axis linearly increases with x, while the c-axis decreases.…”

“…Magnetic phase diagram as a function of temperature and concentration. P, S and CAF stand for the paramagnetic state, the spin-singlet state, and the collinear type AFM state, respectively [40].…”