Determinant influence of surfaces on the Co clustering trend at ZnO

Abstract

Based on ab-initio calculations, we demonstrate that Co tends to cluster at the bulk host favoring [0001] planar structures. However, this tendency is modified at surfaces, involving energy variations an order of magnitude larger than in the bulk. The energy cost to replace Zn by Co, either for isolated impurities or for one- and two-dimensional aggregates, is considerably reduced close to both stoichiometric and polar surfaces, evidencing a tendency of Co impurities to approach the ZnO surface. The formation of Co aggregates strongly depends on the crystallographic termination, leading to the suppression of the Co clustering trend at the O-ended (0001¯).

Elucidating the Structure and Chemical State of Co Growth on the ZnO(101̅0) Surface

“…Compared to polar surfaces, ZnO(0001) and ZnO(0001̅), ZnO(101̅0) has a unique surface structure, which is characterized by the Zn–O dimer rows directed along the [12̅10]. Diffusion of adatoms on the (101̅0) surface is, therefore, constrained along the dimer rows. , In addition, the ab initio calculations of Co on ZnO surfaces suggest that the growth of Co adatoms prefer a disperse distribution on the ZnO(101̅0) surface, but the formation of the Co cluster on ZnO(0001̅) is favored. Therefore, the distinct growth mode of Co on the polar ZnO surface and on the nonpolar ZnO(101̅0) surface is observed.…”

A new diluted magnetic semiconductor based on the expanded phase of ZnS: surmounting the random distribution of magnetic impurities

“…6 A major obstacle has been identified as the random distribution or clustering of the magnetic impurities, namely, spinodal decomposition due to strong attractive interactions between impurities. 6,[12][13][14] Although the phase separation shows super-paramagnetism (i.e., T C = 0) because produced nano-magnets are well separated and have no magnetic correlation each other, ferromagnetic (hysteretic) behaviour in the magnetization process at a finite temperature can be observed due to the blocking effect. [15][16][17][18] Therefore, many experimentalists confuse ''the high T C in the ferromagnetism'' and ''the highblocking temperature in the super-paramagnetism 19 ''.…”