Coexistence of ferromagnetism and superconductivity in Cu-rich lanthanum Cu-oxides

We have measured the zero field and field cooled magnetization of the lightly oxygen doped Cu-rich La₂CuO_4+δ in a wide temperature range (5 K to 350 K). The data together with the evolution of the magnetic hyteresis loop suggest that the ferromagnetism with Curie temperature of 280 K coexists with superconductivity below the transition temperature ∼ 34 K. The coexistence occurs in the hole-rich clusters of size ≤ 150 nm, which are electronic phase separated from the hole-poor antiferromagnetic background.