Effect of cobalt doping on the magnetic properties of the spin-Peierls cuprate CuGeO3

The magnetization of single crystals in the system (Cu1-xCox)GeO3 has been measured for compositions in the range 0.000 less than or equal to x less than or equal to 0.0547. These crystals exhibit paramagnetic behavior, which has been fit with a Curie-Weiss expression to determine the effective moment (mu(eff)) along the three principle crystal directions. For x less than or equal to 0.0225, the spin-Peierls transition is apparent in the magnetization data, with the transition temperature (T-sp) decreasing with increased cobalt doping. For x greater than or equal to 0.0204, an anisotropic magnetic transition occurs below 6 K, and is attributed to three-dimensional long-range antiferromagnetic ordering. When the field is directed along the c axis, spin-flop behavior is observed at a critical field [H-c(x,T)] for temperatures less than the Neel temperature (T-N). Due to the strong paramagnetism in this system, T-N and T-sp as a function of cobalt concentration were measured with single-crystal microcalorimetry. The effects of cobalt doping are discussed with respect to recent reports of Zn, Si, and Ni doping. [S0163-1829(97)03841-1].