COMPLEX SUSCEPTIBILITY OF YBA2(CU1-XCOX)3OY

The superconducting transition of YBa2(Cu1-xCo(x))3O(y) compounds was measured in terms of complex susceptibility, chi = chi'-i-chi". Samples were prepared in two different ways in the range of 0 less-than-or-equal-to x less-than-or-equal-to 1/3. Group I was fabricated by the ordinary oxidization treatment (slow cooling from 850-degrees-C in flowing O2 gas). Group II was prepared by heating in flowing N2 gas at 800-degrees-C for 20 h, followed by slow cooling to room temperature in the same atmosphere and then by annealing in flowing O2 gas below 400-degrees-C for more than 20 h. The transition curves observed for the samples of the two different groups seem to be essentially the same, except the transition temperature. However, careful examinations of the profiles of chi have revealed that the substituted Co atoms in group II cluster to some degree in the Cul-O planes, although the degree of clustering is not distinctive as in the Fe-doped samples.