Electronic and magnetic properties of the high- T c superconductor EuBa 2 Cu 3 O x

Electrical resistivity and magnetic susceptibility show that single phase EuBa2Cu3O x becomes superconducting at 94 K. Magnetization and magnetoresistivity yield a lower critical field of Hc1≃500 G and a variation ofT c with magnetic field of dT c /dH≃1 K/T. The high temperature resistivity shows that at about 700 K due to oxygen loss the sample is driven into a semiconducting state, in which the superconductivity is destroyed. The normal state magnetic susceptibility measured in the superconducting and in the oxygen degased, semiconducting sample indicates that the sample is paramagnetic in the normal state. This paramagnetism is larger than the one expected for trivalent Eu and therefore has to be attributed in part to a magnetic moment on Cu. Eu is found to be stable trivalent between 300 and 4.2 K through Mosbauer-spectroscopy.