Effects of intrabilayer coupling on the magnetic properties of YBa₂ Cu₃O₆

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/T_2G. 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/T_2G, and it is suggested that measurements of this quantity at high temperatures can reveal the strength of the intrabilayer coupling in YBa₂Cu₃O₆.