1. National Institute of Materials Physics, 405A Atomistilor Street, Magurele 077125, Romania
2. Faculty of Physics, University of Bucharest, 405 Atomistilor Street, Magurele 077125, Romania
3. National Institute for Research and Development in Optoelectronics, 409 Atomistilor Street, Magurele 077125, Romania
4. Institute of Physical Chemistry of the Romanian Academy, 202 Splaiul Independentei, Bucharest 060021, Romania
5. Peter Grünberg Institut 9 (PGI 9) and JARA Fundamentals of Future Information Technologies, Forschungszentrum Jülich, Jülich 52425, Germany
6. Academy of Romanian Scientists, 54 Splaiul Independentei, Bucharest 050094, Romania