1. Peter Grünberg Institut, Quanten-Theorie der Materialien, Forschungszentrum Jülich and JARA; D-52425 Jülich Germany
2. Institute for Physics and Chemistry of Solid State, Uzhgorod National University; 88000 Uzhgorod Ukraine
3. Faculty of Physics, Vilnius University, Sauletekio 9/3; LT-10222 Vilnius Lithuania