Chemical Manipulation of High-TCFerromagnetism in ZnO Diluted Magnetic Semiconductors

Magnetic Properties of ZnO Nanoparticles

“…Moreover, there is a perfect correlation in the evolution of these measured properties with the capping molecule: THIOL sample shows the largest alteration of the electronic structure as evidenced by the highest XANES absorption, the absence of PL emission (totally quenched by appearance the new surface states) and the largest magnetic moments (despite the diamagnetic character of ZnO). On the contrary, the TOPO sample presents the electronic configuration more similar to bulk ZnO as confirms the smallest XANES absorption (less charge transfer), the most intense PL Previous experiments on DMS demonstrates that when both contributions are present they are coupled [7,8]. Actually, the incorporation of magnetic impurities into the semiconductor matrix, besides the presence of its magnetic moment, represents an alteration of the semiconductor energy levels.…”

“…For most of the experimental results doubts arose about the real origin of magnetism [4,5,6]. The most recent and outstanding works on this field showed that the magnetic properties are not exclusively related to the presence of the magnetic ions but strongly determined by the defects in the host matrix [7,8,9,10,11,12]. For instance, Kittisltved et al [7,8] showed that Mn:ZnO nanoparticles and thin films show room temperature (RT) ferromagnetism when doped p-type defects, while other capping that introduce n-type defects leads to no RT ferromagnetism.…”

Role of defects in ferromagnetism inZn1−xCoxO: A hybrid density-functional study

“…The result that N O promotes ferromagnetism in Zn 1−x Co x O differs from the experimental finding that N capping of Zn 1−x Co x O nanocrystals containing 3.5% Co results in paramagnetic nanocrystals while O capping of these nanocrystals results in weak ferromagnetism. 6 …”

“…A double-exchange mechanism of ferromagnetic coupling in Zn 1−x Co x O and Zn 1−x Mn x O has been outlined, for example by Petit et al 18 or Kittilstved et al, 6,69 in which certain charge fluctuations are only permitted for the ferromagnetic state. These charge fluctuations generally lower the total energy, and changes to the energy and wave function can be estimated using perturbation theory.…”

“…[2][3][4][5][6] Electron paramagnetic resonance ͑EPR͒ measurements show that it is possible to produce Zn 1−x Co x O with x ഛ 0.1 ͑Refs. 7-9͒ in which Co is substituted for Zn rather than forming clusters.…”