Hole doping by Li substitution and antiferromagnetism in YBa

The magnetic structure of tetragonal insulating YBa2Cu$_{3-x}$LixOy has been studied as a function of x and y. The Néel temperature and the mean ordered magnetic moment on the Cu2 sites were determined by neutron powder diffraction measurements. The decrease of these two parameters as compared to YBa2Cu3O6 is much stronger for lithium than for zinc substitution. The difference is quantitatively explained by the presence of holes created in the CuO2 planes. These holes arise from the substitution of plane Cu2+ by Li+. We suggest an explanation why such holes are not seen for the same substitution of plane Cu2+ by Li+ in orthorhombic superconducting YBa2Cu$_{3-x}$LixO$_{7-\delta}$