Effects of intrabilayer coupling on the magnetic properties of YBa2Cu3O6.

A two-layer Heisenberg antiferromagnet is studied as a model of the bilayer cuprate YBa2Cu3O6. Quantum Monte Carlo results are presented for the temperature dependence of the spin correlation length, the static structure factor, the magnetic susceptibility, and the 63Cu NMR spin-echo decay rate 1/T2G. As expected, when the ratio J2/J1 of the intrabilayer and in-plane coupling strengths is small, increasing J2 pushes the system deeper inside the renormalized classical regime. Even for J2/J1 as small as 0.1 the correlations are considerably enhanced at temperatures as high as T/J1 ≈ 0.4− 0.5. This has a significant effect on 1/T2G, and it is suggested that measurements of this quantity at high temperatures can reveal the strength of the intrabilayer coupling in YBa2Cu3O6.