[1] Univ Johannesburg, Dept Phys, POB 524,Auckland Pk, ZA-2006 Johannesburg, South Africa
[2] Van Der Waals Zeeman Inst, Inst Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands
[3] Max Planck Inst Solid State Res, Heisenbergstr 1, D-70569 Stuttgart, Germany
[4] Louisiana State Univ, Dept Phys & Astron, Baton Rouge, LA 70803 USA