On the superconducting and magnetic properties of HoNbO3-delta and EuNbO3-delta complex oxides

Complex oxide compounds of niobium and rare-earth elements, HoNbO3-delta an d EuNbO3-delta, have been synthesized, and their magnetic and superconducti ng properties have been studied. Both these compounds are superconductors w ith transition temperatures T-c = 15 and 6 K, respectively. The properties of these compounds are strongly affected by the content of oxygen, in parti cular, T-c drops with this parameter. The compounds are paramagnetic at tem peratures higher than T-c. The HoNbO6-delta magnetic susceptibility follows the Curie law, and the effective susceptibility of Ho ions mu (eff) = 9.0. The EuNbO3-delta susceptibility is described by the Curie-Weiss law with t he Curie temperature Theta (c) = 4.4 K, and the effective susceptibility of Eu ions mu (eff) = 6.5. The possibility of coexistence of superconductivit y and ferromagnetism in EuNbO3-delta is discussed. (C) 2001 Elsevier Scienc e B.V. All rights reserved.