Room-temperature ferromagnetism in nanoparticles of superconducting materials

Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (T-c, = 91 K) exhibit ferromagnetism at room temperature while the bulk YBCO, obtained by heating the nanoparticles at high temperature (940 degrees C), shows a linear magnetization curve. Across the superconducting transition temperature, the magnetization curve changes from that of a soft ferromagnet to a superconductor. Furthermore, our experiments reveal that not only nanoparticles of metal oxides but also metal nitrides such as NbN (Tc = 6-12 K) and delta-MoN (T-c - 6K) exhibit room-temperature ferromagnetism. (C) 2007 Elsevier Ltd. All rights reserved.