TRANSITION FROM DIMERIZATION TO ANTIFERROMAGNETIC ORDER IN QUASI-ONE-DIMENSIONAL CA0.83CUO2

Magnetic susceptibility and torque anisotropy were measured on the nov el quasi-one-dimensional cuprate Ca0.83CuO2-delta. Substantial hole do ping between 0.27 and 0.36 holes/Cu can be achieved by changing the ox ygen content. This strongly influences dimerization, which originates from a modulated exchange coupling in the CuO2 chains. Another interes ting result is the unexpected transition at T = 12.2(1) K into an anti ferromagnetic ordered state in spite of the high doping. By torque ana lysis the existence of an easy axis in this ordered state was clearly demonstrated and its orientation determined.