Co-appearance of high-<i>T_c</i> superconductivity and ferromagnetism in a Ca₂RuO₄ nanocrystal

We report the realization of high-temperature superconductivity in Ca₂RuO₄ nanofilm single crystals. Ca₂RuO₄ thin film with the highest transition temperature Tc (midpoint) of 64 K exhibits zero resistance in electric transport measurements. The superconducting critical current exhibited a logarithmic dependence on temperature and was enhanced by an external
magnetic field. Magnetic measurements revealed a ferromagnetic transition at 180 K and diamagnetic magnetization due to superconductivity. Our results suggest the co-appearance of superconductivity and ferromagnetism in Ca₂RuO₄ nanofilm crystals. We also found that the induced bias current and the tuned film thickness caused a superconductor-insulator transition.