Room-temperature ferromagnetism in nanoparticles of superconducting materials

Nanoparticles of superconducting YBa 2 Cu 3 O 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 ∘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 ( T c = 6 – 12 K ) and δ -MoN ( T c ∼ 6 K ) exhibit room-temperature ferromagnetism.