Quasi-one-dimensional magnetism in the spin-$\frac12$ antiferromagnet BaNa$_{2}$Cu(VO$_{4}$)$_{2}$

Abstract

We report synthesis and magnetic properties of quasi-one-dimensional spin-1 2 Heisenberg antiferromagnetic chain compound BaNa2Cu(VO4)2. This orthovanadate has a centrosymmetric crystal structure, C2/c, where the magnetic Cu 2+ ions form spin chains. These chains are arranged in layers, with the chain direction changing by 62 • between the two successive layers. Alternatively, the spin lattice can be viewed as anisotropic triangular layers upon taking the inter-chain interactions into consideration. Despite this potential structural complexity, temperature-dependent magnetic susceptibility, heat capacity, ESR intensity, and NMR shift agree well with the uniform spin-1/2 Heisenberg chain model with an intrachain coupling of J/kB ≃ 5.6 K. The saturation field obtained from the magnetic isotherm measurement consistently reproduces the value of J/kB. Further, the 51 V NMR spin-lattice relaxation rate mimics the 1D character in the intermediate temperature range, whereas magnetic long-range order sets in below TN ≃ 0.25 K. The effective interchain coupling is estimated to be J ⊥ /kB ≃ 0.1 K. The theoretical estimation of exchange couplings using band-structure calculations reciprocate our experimental findings and unambiguously establish the 1D character of the compound. Finally, the spin lattice of BaNa2Cu(VO4)2 is compared with the chemically similar but not isostructural compound BaAg2Cu(VO4)2.