1. CNR‐ISMN Via Piero Gobetti 101 Bologna 40129 Italy
2. Department of Physics and Astronomy A. Righi University of Bologna via Berti Pichat 6‐2 Bologna I‐40127 Italy
3. Department of Mathematical Physical and Computer Sciences University of Parma Parco Area delle Scienze 7/A Parma 43124 Italy
4. Department of Materials Science and Engineering National Chung Hsing University 145 Xingda Rd. Taichung City 402 Taiwan