Magnetic properties of theS=12quasi-one-dimensional antiferromagnetCaCu2O3

We report single-crystal growth and magnetic susceptibility and neutron diffraction studies of the $S=\frac{1}{2}$ quasi-one-dimensional antiferromagnet ${\mathrm{CaCu}}_2{\mathrm{O}}_3.$ The structure of this material is similar to that of the prototype two-leg spin-ladder compound ${\mathrm{SrCu}}_2{\mathrm{O}}_3.$ However, the Cu-O-Cu bond angle in the ladder rungs in ${\mathrm{CaCu}}_2{\mathrm{O}}_3$ is equal to $123°,$ and therefore the magnetic interaction along the rung is expected to be much weaker in this material. At high temperatures, the magnetic susceptibility of ${\mathrm{CaCu}}_2{\mathrm{O}}_3$ can be decomposed into a contribution from one-dimensional antiferromagnetic chains or finite-size chain segments together with a weak Curie contribution. The intrachain magnetic exchange constant $J_{\Vert },$ determined from the magnetic susceptibility measurements, is $2000\pm 300$ K. ${\mathrm{CaCu}}_2{\mathrm{O}}_3$ undergoes a Néel transition at $T_N=25\mathrm{}$ K with ordering wave vector of [0.429(5), $\frac{1}{2},$ $\frac{1}{2}].$ The magnetic structure is incommensurate in the direction of the frustrated interchain interaction. Weak commensurate magnetic Bragg peaks with the reduced wave vector $(\frac{1}{2},$ $\frac{1}{2},$ $\frac{1}{2})$ are also observed below $T_N.$ Application of a magnetic field induces a metamagnetic transition at which the incommensurability of the magnetic structure is substantially reduced. Above the transition field, the material possesses only short-range magnetic order, and no well defined temperature-driven transition is observed.