ANTIFERROMAGNETISM IN YBA2CU3O6+X - GA AND ZN SUBSTITUTIONS .2. ZERO-FIELD NMR OF THE CU MAGNETIC SITES

We present an extensive study of the antiferromagnetic state of YBa2Cu3O6+x (0<x<0.3) through 63Cu zero field nuclear magnetic resonance (ZFNMR). Our experiments clearly demonstrate that hole doping in the CuO2 planes occurs only for x > 0.2 and that the nuclear spin T1 is very short nearby doped holes. As for static magnetic disorder, we show that ZFNMR is a very local in-plane probe nearly insensitive to the stacking of the CuO2 antiferromagnetic sheets. No magnetic disorder occurs for x<0.2 within CuO2 planes. For x > 0.2 a comparison with muon and neutron results is presented. Cu substitution by Ga and Zn do not affect markedly the AF order of the CuO2 sheet while intensity measurements clearly demonstrate that Zn does not substitute appreciably on the Cu(2) site. © 1990.