Quasi-one-dimensional magnetism in the spin- 1 2 antiferromagnet BaNa 2 Cu ( VO 4 ) 2

We report synthesis and magnetic properties of quasi-one-dimensional spin-$\\frac{1}{2}$ Heisenberg antiferromagnetic chain compound ${\\mathrm{BaNa}}_{2}\\mathrm{Cu}{({\\mathrm{VO}}_{4})}_{2}$. This orthovanadate has a centrosymmetric crystal structure, $C2/c$, where the magnetic ${\\mathrm{Cu}}^{2+}$ ions form spin chains. These chains are arranged in layers, with the chain direction changing by ${62}^{\\ensuremath{\\circ}}$ between the two successive layers. Alternatively, the spin lattice can be viewed as anisotropic triangular layers upon taking the interchain interactions into consideration. Despite this potential structural complexity, temperature-dependent magnetic susceptibility, heat capacity, electron spin resonance intensity, and nuclear magnetic resonance (NMR) shift agree well with the uniform spin-$1/2$ Heisenberg chain model with an intrachain coupling of $J/{k}_{\\mathrm{B}}\\ensuremath{\\simeq}5.6$ K. The saturation field obtained from the magnetic isotherm measurement consistently reproduces the value of $J/{k}_{\\mathrm{B}}$. Further, the $^{51}\\mathrm{V}$ NMR spin-lattice relaxation rate mimics the one-dimensional character in the intermediate temperature range, whereas magnetic long-range order sets in below ${T}_{\\mathrm{N}}\\ensuremath{\\simeq}0.25$ K. The effective interchain coupling is estimated to be ${J}_{\\ensuremath{\\perp}}/{k}_{\\mathrm{B}}\\ensuremath{\\simeq}0.1$ K. The theoretical estimation of exchange couplings using band-structure calculations reciprocate our experimental findings and unambiguously establish the one-dimensional character of the compound. Finally, the spin lattice of ${\\mathrm{BaNa}}_{2}\\mathrm{Cu}{({\\mathrm{VO}}_{4})}_{2}$ is compared with the chemically similar but not isostructural compound ${\\mathrm{BaAg}}_{2}\\mathrm{Cu}{({\\mathrm{VO}}_{4})}_{2}$.