[1] Department of Physics, University of Cape Town, 7701, Rondebosch, South Africa
[2] Department of Physics, Univ. of the N., QwaQwa Campus, 9866, Phutaditjhaba, South Africa
[3] Univ. der Bundeswehr München, Fachbereich Elektrotechnik, Wissenschaftliche Einrichtung Physik, D-85577 Neubiberg, Germany