1. Laboratory of Magnetism and Superconductivity, National Institute of Materials Physics, 409 Atomistilor St., P.O. Box MG–36, RO-77125 Magurele, Romania
2. Department for Optospintronics, National Institute of R&D for Optoelectronics INOE 2000, 409 Atomistilor St., P.O. Box MG–5, RO-77125 Magurele, Romania
3. National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, P.O. Box MG–36, RO-77125 Magurele, Romania