  Using thermodynamic measurements and density-functional band-structure
calculations, we explore magnetic behavior of SrCuTe2O6. Despite being a
structural sibling of a three-dimensional frustrated system PbCuTe2O6, this
spin-1/2 quantum magnet shows remarkably different low-temperature behavior.
Above 7 K, magnetic susceptibility of SrCuTe2O6 follows the spin-chain model
with the antiferromagnetic intrachain coupling of J = 49.3 K. We ascribe this
quasi-one-dimensional behavior to the leading third-neighbor coupling that
involves a weakly bent Cu--O......O--Cu superexchange pathway with a short
O.....O contact of 2.79 \AA. Below 5 K, SrCuTe2O6 undergoes two consecutive
magnetic transitions that may be triggered by the frustrated nature of
interchain couplings. Field dependence of the magnetic transitions (phase
diagram) is reported.
