ANTIFERROMAGNETISM IN YBA2CU3O6+X - GA AND ZN SUBSTITUTIONS .1. Y-89 NMR DETERMINATION OF THE NEEL TEMPERATURE

The Néel temperature TN of YBa2(Cu1-yMy)3O6+x for pure (0<x<0.3) and M = Zn and Ga doped samples (x<0.2) has been measured from the abrupt increase of the 89Y NMR width with decreasing T. A rather weak variation of TN and of the NMR width in the antiferromagnetic state has been detected upon Zn or Ga doping. This leads us to conclude that a majority of Zn atoms are substituted on the Cu (1) site. In the absence of paramagnetic moments on the Cu (1) layer, the magnetic interactions between CuO2 bilayers might be assigned to dipole-dipole couplings, except if the correlation length for the 2D bilayers has a much steeper T dependence than for La2CuO4. A detailed analysis of the hole doping in the pure compounds is attempted. © 1990.