Coexisting ferromagnetism and superconductivity in hybrid rutheno-cuprate superconductors

We report the observation of microscopically coexisting ferromagnetism and superconductivity in a hybrid ruthenocuprate RuSr2GdCu2O8, with T-c less th an or equal to 40K By means of various substituents it is established that the superconductivity originates in the CuO2 planes and the ferromagnetism in the RuO2 planes, as expected. Muon spin relaxation measurements show tha t the ferromagnetism, with Curie temperature T-M = 132K, is microscopically uniform and originates from the entire sample bulk. This is probably the f irst confirmed example of uniform microscopic coexistence of superconductiv ity and atomic ferromagnetism. The material is determined from thermopower measurements to be an underdoped cuprate with a projected T-c,T-max = 90-10 0h; typical of a two-layer cuprate. The oxygen isotope effect exponent of a lpha(Tc) = 1.7 is the largest observed in the high-T-c cuprates. These mate rials are expected to provide a rich source of new physics and applications .