Competition between ferromagnetism and superconductivity in GdBa2Cu3O7-x/La0.7Sr0.3MnO3 bilayers with varying thickness

We investigated the effect of the thickness of superconducting layer on the competition between ferromagnetism and superconductivity. The epitaxial bilayer systems consisting of GdBa2Cu3O7-x (GdBCO) with varying thickness and La0.7Sr0.3MnO3 (LSMO) were grown on (001) SrTiO3 (STO) substrate. From the spectroscopic measurements, we observed an existence of a possible structural coupling between the GdBCO and the LSMO layers. The structural coupling is found to depend on the GdBCO thickness and to induce different types of strain on both layers, leading to the competition between the ferromagnetic and the superconducting orders. With respect to the flux pinning, an additional pinning contribution besides magnetic pinning induced by LSMO is emerged by the structural coupling, which is attributed to local atomic disorder. Controlling the thickness of GdBCO modifies the structural coupling and consequently, the degree of additional pinning contribution aroused by disorder on the CuO2 plane can be adjusted. An appropriate structure with a certain thickness amplifies the hybrid effect of magnetic pinning and additional pinning, resulting in an enhancement of the critical current density at high magnetic fields. Our findings suggest a possibility of controlling complex flux pinning through an optimization of structural coupling between the GdBCO and the LSMO layers.