1. Institute of Physics of the ASCR, v.v.i., Na Slovance 2, 18221 Prague 8, Czech Republic, Czech Geological Survey, Geologická 6, 152 00 Prague 5, Czech Republic, National Institute for Interdisciplinary Science and Technology, Trivandrum 695019, India, and Institute of Inorganic Chemistry of the ASCR, v.v.i., 250 68 Husinec-Řež 1001, Czech Republic