COEXISTENCE OF MAGNETIC-ORDERING INDUCED BY NI SPINS AND SUPERCONDUCTIVITY IN NI-SUBSTITUTED YBA2CU3O7-CU NQR STUDY

From the Cu NQR measurements in the superconducting state of Ni-substi tuted YBa2(Cu1-xNix)(3)O-7, it has been found that the nuclear spin-la ttice relaxation rate, 1/T-1 and the spin echo decay rate, 1/T-2 of Cu -63 are Largely enhanced around T-M = 2.5 and 3.5 K for 7 and 10% Ni d oping, respectively. Below T-M, the Cu NQR spectrum has revealed the p resence of distributed internal fields at Cu nuclei in the CuO2 plane with a maximum value of similar to 2.5 kOe. From these results, the ma gnetic ordering is concluded to take place by the indirect exchange co upling among Ni moments with S = 1/2 mediated by the antiferromagnetic Cu spin polarization around Q = (pi/a,pi/a) in the CuO2 plane. We pro pose that the superconductivity coexist with the magnetic ordering due to the d wave nature with node line around Q = (pi/a,pi/a).