Magnetic order in the hole-doped two-leg ladder compound Sr2.5Ca11.5Cu24O41: Evidence from Cu-NMR and -NQR studies on a single crystal

We report from Cu-NQR and -NMR experiments that hole-doped two-leg ladder c ompound Sr-2.5- Ca11.5Cu24O41 comprising Cu2O3 ladders and CuO2 chains reve als three-dimensional (3D) magnetic order below T-M = 2.2K. We found that s mall moments similar to 0.02 mu(B) are spontaneously ordered on the ladders , whereas large moments similar to 0.56 mu(B) are on the magnetic Cu sites occupying about one-fourth of the chain Cu sites. It is suggested that this 3D magnetic order is a cooperative phenomenon driven by the formation of p inned charge density wave-like state on the ladders which the optical condu ctivity measurement has clarified. [S0031-9007(99)09206-6].