1. Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein ZA9300, South Africa
2. DST/CSIR National Centre for Nano-Structured Materials, Council for Scientific Industrial Research, Pretoria 0001, South Africa
3. Department of Physics, University of Limpopo, Private Bag X1106, Sovenga 0727, South Africa
4. Highly Correlated Matter Research Group, Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa