LOCAL MOMENT FORMATION AT CU(2) SITES AROUND CO ATOM IN YBA2(CU1-XCOX)3O7-NQR(Y STUDIED BY CU)

Cu-NQR spectra in YBa2(Cu1-xCox)3O7+y were investigated systematically from x=0 to 0.18. In the normal state, T=100 K, the integrated intens ities of the spectra for both Cu(I) and Cu(2) sites decrease rapidly w ith increasing x, which indicates that the large region around Co atom extending to 4 approximately 5th n.n. in Cu (1)-chain plane and 3rd - 4th n. n. in Cu(2)O2 plane are wiped out from observation. From tempe rature dependence of the spectra, the magnetic ordered state associate d with Co moments is confirmed to coexist with the superconducting sta te. The magnetic transition temperature, T(M), is estimated from tempe rature dependence of the resonance intensities. At 1.5 K, the abnormal ly broad spectra ranging from 6 to 130 MHz appear, indicating the loca l moment formation at Cu(2) sites in the region wiped out at 100 K. So me discussions are made on the origins of the destruction of the super conductivity from the experimental results.