Rare earth substituted YBa2Cu3O x

We present some selected results obtained using rare earth Mössbauer spectroscopy, on YBa₂Cu₃O _x partially and/or totally substituted by Yb³⁺, Er³⁺ or Dy³⁺. We report measurements of the single ion crystal field anisotropy and of the size, direction and ordering temperature of the rare earth sublattice magnetic moments. We use dilute¹⁷⁰Yb³⁺ ions to probe both the Cu(2) derived internal (molecular) fields and the fluctuation frequencies of the short range correlated Cu(2) moments. We monitor these frequencies as the carrier level is changed up towards the threshold needed to stabilise superconductivity.