Correlation Between Ferromagnetism and Superconductivity at Interfaces of La2/3Ca1/3MnO3/YBa2Cu3O7−δ/La2/3Ca1/3MnO3 Trilayers Grown by dc Sputtering

In this work, we study the magnetoelectrical properties of La2/3Ca1/3MnO3/YBa2Cu3O7−δ /La2/3Ca1/3MnO3 heterostructures grown by means of high oxygen-pressure dc sputtering onto (001)-oriented SrTiO3 substrates. The test heterostructures are composed of ferromagnetic layers of constant thicknesses (∼280 unit cells, ∼110 nm) and superconducting interlayers with thicknesses ranging between 5 (∼6 nm) and 15 unit cells (∼17 nm). Transport measurements show a strong suppression of the superconducting properties when the thickness of the YBa2Cu3O7−δ interlayer is reduced to a value below 10 unit cells. Magnetic measurements show superconducting transition in junctions with YBa2Cu3O7−δ interlayers with thicknesses larger than ∼15 unit cells. The observed difference in the values of the superconductivity onset when determined by electrical and magnetic measurements might be related with the presence of a spontaneous vortex phase in the temperature range around the superconducting transition.