Cu NMR IN THE SUPERCONDUCTING STATE OF ReBa2Cu3Ox

Abstract

Cu NMR of the high-Tc magnetic superconductor of GdBa2Cu3Ox (x ~ 6.7) has been investigated at both low (~4.5 kOe) and high (~130 kOe) external fields. In low external field, the observed positive sift of about 400 Oe at 1.3 K was found to be due to antiferromagnetically ordered Gd moments, which align antiparallel to the nearest neighbors with a slight canting induced by the external field. In high external field, the Cu NMR spectra of both Cu–O chain (site I) and plane (site II) were observed at 131 MHz below 4.2 K. The induced field is estimated to be 1.16 kOe at Cu site II through the uniform spin polarization of the conduction electrons by the Gd spin moment. Thus the observed weak interaction between the Gd magnetic moment and the conduction electron in the Cu–O plane is considered to be responsible for the fact that Tc does not decrease significantly even when Y is replaced by magnetic ions.