[1] IPICyT, Adv Mat Dept, San Luis Potosi 78216, Mexico
[2] Arizona State Univ, Sch Mat, Tempe, AZ 85287 USA
[3] Arizona State Univ, Dept Phys, Tempe, AZ 85287 USA
[4] Oak Ridge Natl Lab, Oak Ridge, TN 37831 USA
[5] Catholic Univ Louvain, PCPM & ETSF, B-1348 Louvain, Belgium