Tellurium-bridged two-leg spin ladder inBa2CuTeO6

Abstract

We present single-crystal growth and magnetic property studies of tellurium-bridged copper spin-$\frac{1}{2}$ system ${\mathrm{Ba}}_{2}{\mathrm{CuTeO}}_{6}$. The spin-exchange interaction among copper spins via $\mathrm{Cu}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Te}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Cu}$ super-superexchange route leads to a novel two-leg spin ladder system. Spin susceptibility $\ensuremath{\chi}(T)$ data indicate that the triclinic ${\mathrm{Ba}}_{2}{\mathrm{CuTeO}}_{6}$ undergoes a stepwise crossover for exchange couplings revealed by a broad maximum of $\ensuremath{\chi}(T)$ near ${T}_{max}\ensuremath{\sim}75$ K and an anisotropic cusp in $\frac{d\ensuremath{\chi}}{dT}(T)$ at ${T}_{N}\ensuremath{\sim}15$ K to signify a three-dimensional (3D) antiferromagnetic long-range ordering (LRO). The 3D LRO has been suggested from the anisotropic behavior of $\ensuremath{\chi}(T)$ with strong $c$-axis spin anisotropy and the signature of spin-flop transition from the isothermal magnetization below ${\mathit{T}}_{N}$. Analysis of magnetic heat capacity (${C}_{m}$) at ${T}_{N}\ensuremath{\sim}15$ K indicates that most of the spin entropy $(\ensuremath{\sim}92%)$ has already been released above ${T}_{N}$, which supports the picture of consecutive spin entropy reduction upon cooling with Te-bridged two-leg spin ladder system with strong intraladder and interladder couplings. Theoretical $\mathrm{DFT}+U$ calculations have been performed to search for the ground-state magnetic configuration and also to evaluate exchange-coupling constants that support the magnetic model deduced from the combined spin susceptibility and crystal structure symmetry analysis.