1. State Key Lab of Crystal Materials; Shandong University; Jinan 250100 Shandong P. R. China
2. Key Lab for Colloid and Interface Chemistry of State Educating Ministry; School of Chemistry and Chemical Engineering; Shandong University; Jinan 250100 Shandong P. R. China
3. Peter Grünberg Institut and Institute for Advanced Simulation; Research Centre Jülich; Jülich 52425 Germany