The interplay between the naturally antagonistic superconductivity and ferromagnetism phenomena gives rise to rich physical properties, cooperative interactions and unusual behaviours. In this work, we have explored two different systems showing the Superconductor-Ferromagnetic (SC-FM) coexistence; (i) artificial nanoscale hybrid systems formed by a soft ferromagnetic thin film interacting with YBa2Cu3O7-d (YBCO) superconducting dots (ii) Ferromagnetic clusters embedded within uniform YBCO films.
The first approach consists on a specially designed SC-FM hybrid system as a novel way for robustly encoding and modify nontrivial magnetic states. The SC-FM hybrids consist of high-temperature YBCO superconducting dots, patterned with different shapes, and covered by a continuous thin ferromagnetic Permalloy (Py) layer. A large manifold of non-singular magnetization patterns (imaged by X-ray PEEM using XMCD) were imprinted in a Py layer by using the remanent stray field generated by the SC dots. The obtained configurations include head-to-head magnetic structures yielding a monopolar field with controlled polarity. Micromagnetic simulations confirmed that the magnetic structures appearing in the FM layer are arising and governed from the stray fields created by SC dots. The general approach presented may be used to provide a large number of spin textures of interest in a well-controlled way.
The coexistence of SC and FM phases in uniform materials requires singular conditions and occurs only in a very limited number of systems. In the second approach here presented we show the spontaneous formation of ferromagnetic clusters embedded within YBCO SC films with a high concentration of Y124 intergrowths, the commonest YBCO defect. Our work was able to connect a dilute magnetic behavior, a macroscopic phenomenon, explored using XMCD measurements with atomic-scale structure and chemistry obtained using STEM imaging and spectroscopy, both of which are tied up through DFT calculations. We used all these techniques to unveil the existence of a magnetic moment associated to a complex point defect (2 V Cu +3 V O ) generated within the Y124 intergrowth. The ferromagnetic state of the defect cluster coexist with the superconducting state and may cause local pair breaking that would provide extra vortex pinning in the YBCO films. Moreover our results may be generalized to other defective perovskite-based systems, being a novel soured of multifuncionality.
1 Institut de Ciència de Materials de Barcelona ICMAB-CSIC, Spain
2 Helmholtz-Zentrum Berlin für Materialien und Energie, Germany
3 Grup d’Electromagnetisme, Departament de Fisica, Universitat Autonoma de Barcelona, Spain
4 Neutron Sciences Directorate, Oak Ridge National Laboratory, USA
5 Department of Physics and Astronomy Vanderbilt University, USA
6 Materials Science and Technology Division, Oak Ridge National Laboratory, USA
7 Escola Universitària Salesiana de Sarrià, Barcelona 08017, Spain
8 Laboratorio de Microscopías Avanzadas Instituto de Nanociencia de Aragón – ARAID Universidad de Zaragoza, Spain
9 Universidad Complutense de Madrid, Spain
10 ALBA Synchrotron Light Source, Spain
11 Department of Materials Science and Engineering National University of Singapore, Singapore