1. Department of Magnetic Measurements and Materials, FZU Institute of Physics of the Czech Academy of Sciences Na Slovance 2 182 21 Prague Czech Republic
2. Department of Ultrasonic Methods Institute of Thermomechanics of the Czech Academy of Sciences Dolejškova 5 18200 Prague Czech Republic
3. Institute of Physics of Charles University Faculty of Mathematics and Physics of the Charles University Ke Karlovu 5 12116 Prague Czech Republic