Neutron Scattering Studies of Magnetism in High<i>T</i>_cSuperconductors

Abstract

Results of neutron scattering studies of the magnetic properties of YBa2Cu3O6+x materials are reviewed. At low oxygen concentration, anti-ferromagnetic ordering in the CuO2 sheets has been evidenced. The Néel temperature is around 415 K. With increasing oxygen content, the ordered magnetic moment and the Néel temperature are reduced. Finally, the long range magnetic order disappears for xc = 0.41, which indicates the appearance of a large number of holes in the CuO2 layers. Inelastic neutron scattering measurements of spin waves have established the two-dimensional character of the magnetic couplings in the antiferromagnetic phase. Increasing the hole concentration reduces the spin wave stiffness and close to xc the in-plane spin fluctuations become diffusive.