MAGNETIC BILAYER COUPLING IN YBA2CU3O7

The spin-fluctuation spectrum of an extended t-J model appropriate to bilayer Y-Ba-Cu-0 is investigated within a renormalized-mean-field app roach. Strong antiferromagnetic correlation between bilayers is found. for realistic values of the interplane coupling in a regime where the inplane susceptibility is strongly exchange enhanced even though the a ntiferromagnetic correlation length is short. The influence of spin pa iring on the spin-fluctuation spectrum, in this case via a d-wave orde r parameter, is included. The model predicts a strong energy dependenc e of the modulation in the vicinity of the characteristic energy for s pin fluctuations.