Spin density and form factor measurements on HTSC copper oxides

Polarized neutron investigations on superconducting copper oxides, La2-xSrxCuO4 and YBa2Cu3O6+x, as well as studies of related antiferromagnetic compounds, using unpolarized neutrons, permit to outline some characteristical features of the spin distribution. No covalency on the in-plane oxygens is observed, neither in the antiferromagnetic state, nor in the superconducting state. In superconducting compounds, the in-plane copper displays a small induced magnetic moment, about 10-3μB (H = 5T), almost temperature independent. In YBa2Cu3O6+x, a distinct behaviour is found for the chain copper. The induced spin density in HoBa2Cu3O7 exhibits specific features which are not present in non superconducting HoBa2Cu3O6.5