sup 89 Y NMR study of the exchange coupling constant between the CuO sub 2 layer and the Gd ion in Gd sub x Y sub 1 minus x Ba sub 2 Cu sub 3 O sub 7 minus. delta

Free-induction decays of {sup 89}Y NMR are observed in magnetically dilute alloys Gd{sub {ital x}}Y{sub 1{minus}{ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} for {ital x}=0, 0.005, and 0.01. It is shown that the excess decay by Gd is almost completely due to its direct dipolar interactions. From an analysis of the indirect Ruderman-Kittel-Kasuya-Yosida interaction, the exchange coupling constant is estimated to be less than 0.01 eV.