Room-temperature ferromagnetism in nanoparticles of superconducting materials

摘要

Nanoparticles of superconducting YBa_2Cu_3O_(7-δ) (YBCO) (T_c = 91 K) exhibit ferromagnetism at room temperature while the bulk YBCO, obtained by heating the nanoparticles at high temperature (940℃), 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 (T_c = 6-12 K) and δ-MoN (T_c ～ 6 K) exhibit room-temperature ferromagnetism.