[1] Tech Univ Carolo Wilhelmina Braunschweig, Inst Organ Chem, D-38106 Braunschweig, Germany
[2] Tech Univ Carolo Wilhelmina Braunschweig, Inst Hochfrequenztech, D-38106 Braunschweig, Germany
[3] Phys Tech Bundesanstalt, D-38116 Braunschweig, Germany
[4] Phys Tech Bundesanstalt, Working Grp Electromagnet Fields, D-38116 Braunschweig, Germany
[5] Fraunhofer Inst Appl Solid State Phys, D-79108 Freiburg, Germany