Abstract
We report specific heat, magnetic susceptibility and neutron scattering measurements on the single crystals of Sr 14- x Ca x Cu 24 O 41 . The specific heat data of Sr 2.5 Ca 11.5 Cu 24 O 41 ( x =11.5) showed a sharp phase transition at T N ≈2.3 K, and T N was decreased with decreasing the Ca content x . Susceptibility measurements for x =9, 10 and 11.5 revealed that this phase transition is due to antiferromagnetic ordering. In the neutron scattering experiments for x =10 and 11.5, we observed several Bragg peaks, corresponding to the antiferromagnetic ordering confirmed in the specific heat and susceptibility measurements. A possible magnetic structure on the chain and ladder sites has been proposed. In this system, the singlet state and antiferromagnetic ordering induced by Ca substitution for Sr coexist at ambient pressure and the dissolved hole pairs move under high pressure, leading to the occurrence of superconductivity.
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