Room-temperature ferromagnetism in nanoparticles of superconducting materials

Nanoparticles of superconducting YBa2Cu3O7−δ (YBCO) (Tc=91K) exhibit ferromagnetism at room temperature while the bulk YBCO, obtained by heating the nanoparticles at high temperature (940 ∘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=6–12K) and δδ-MoN (Tc∼6K) exhibit room-temperature ferromagnetism.