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Structural and electronic properties of Eu- and Pd-doped ZnO.

Assadi MH, Zhang Y, Zheng RK, Ringer SP, Li S - Nanoscale Res Lett (2011)

Bottom Line: The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated.The total and partial densities of electron states were also determined for both systems.It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. sean.li@unsw.edu.au.

ABSTRACT
Doping ZnO with rare earth and 4d transition elements is a popular technique to manipulate the optical properties of ZnO systems. These systems may also possess intrinsic ferromagnetism due to their magnetic moment borne on 4f and 4d electrons. In this work, the structural, electronic, and magnetic properties of Eu- and Pd-doped ZnO were investigated by the ab initio density functional theory methods based on generalized gradient approximation. The relative stability of incorporation sites of the doped elements in the ZnO host lattice was studied. The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated. The total and partial densities of electron states were also determined for both systems. It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx.

No MeSH data available.


Related in: MedlinePlus

Total and partial DOS of the ZnO:Eu systems. Representing (a) ZnO:EuZn, (b) ZnO:EuI, (c) ZnO:EuZn + VO, (d) ZnO:EuZn + ZnI systems. The solid black lines and the red-shaded areas represent the total and Eu's partial 4f states, respectively. Also, energy is represented with respect to the Fermi level.
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Figure 2: Total and partial DOS of the ZnO:Eu systems. Representing (a) ZnO:EuZn, (b) ZnO:EuI, (c) ZnO:EuZn + VO, (d) ZnO:EuZn + ZnI systems. The solid black lines and the red-shaded areas represent the total and Eu's partial 4f states, respectively. Also, energy is represented with respect to the Fermi level.

Mentions: To investigate the electronic properties of the ZnO:Eu systems, the total and Eu's 4f partial density of states (DOS) of all configurations were calculated and presented in Figure 2. A general feature of the Eu's 4f states in all configurations is that Eu's 4f states are localized in a narrow impurity band of the width of approximately 1 eV, which is located just below the Fermi level. Such localization of the 4f states indicates that 4f electrons are not affected by the local crystal environment. This point is further reinforced by the Eu's magnetization as presented in Table 1. The spin number (S) of the Eu ions in all configurations is approximately 6.9, very close the spin number of free Eu atoms which indicates the infinitesimal hybridization of Eu's f orbitals with other orbitals in the host crystals. According to Figure 2a, b, in stochiometric systems, ZnO:EuZn and ZnO:EuI, there are minor electronic states available at the Fermi level resulting in limited mobile carriers in those systems. However, this amount of carriers is not sufficient to establish carrier-mediated magnetism in the stochiometric ZnO:Eu systems, and these systems remain paramagnetic [24]. By introducing VO, in the ZnO:EuZn + VO system, the VO's impurity states appear below Eu's 4f states as shown in Figure 2c. Thus, VO does not enhance the carrier concentration in the ZnO:EuZn + VO system either. As shown in Figure 2d in the ZnO:EuZn + ZnI system, ZnI's 4s states appear in a small peak at the Fermi level, partially hybridizing with Eu's 4f states and introducing further carriers at the Fermi level. To investigate the possibility of ferromagnetic coupling in the defective systems, two substitutional Eu ions were located in the supercells. Then the Ef of each system was calculated once for ferromagnetic magnetic alignment (EFM) and once again for antiferromagnetic magnetic alignment (EAFM) of the Eu ions. Finally, ΔE is defined to be EAFM - EFM which is an indicator of ferromagnetic phase stabilization. For Eu ions separated by approximately 3.4 Å (nearest possible distance), ΔE was found to be 21 meV for the ZnO:Eu + ZnI system and 3 meV for the ZnO:Eu + VO system. However, for both systems, the ΔE vanishes when the separation between the Eu ions increases to approximately 6 Å. This trend in ΔE indicates that ZnI induces short range ferromagnetic coupling in the ZnO:Eu system.


Structural and electronic properties of Eu- and Pd-doped ZnO.

Assadi MH, Zhang Y, Zheng RK, Ringer SP, Li S - Nanoscale Res Lett (2011)

Total and partial DOS of the ZnO:Eu systems. Representing (a) ZnO:EuZn, (b) ZnO:EuI, (c) ZnO:EuZn + VO, (d) ZnO:EuZn + ZnI systems. The solid black lines and the red-shaded areas represent the total and Eu's partial 4f states, respectively. Also, energy is represented with respect to the Fermi level.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3211447&req=5

Figure 2: Total and partial DOS of the ZnO:Eu systems. Representing (a) ZnO:EuZn, (b) ZnO:EuI, (c) ZnO:EuZn + VO, (d) ZnO:EuZn + ZnI systems. The solid black lines and the red-shaded areas represent the total and Eu's partial 4f states, respectively. Also, energy is represented with respect to the Fermi level.
Mentions: To investigate the electronic properties of the ZnO:Eu systems, the total and Eu's 4f partial density of states (DOS) of all configurations were calculated and presented in Figure 2. A general feature of the Eu's 4f states in all configurations is that Eu's 4f states are localized in a narrow impurity band of the width of approximately 1 eV, which is located just below the Fermi level. Such localization of the 4f states indicates that 4f electrons are not affected by the local crystal environment. This point is further reinforced by the Eu's magnetization as presented in Table 1. The spin number (S) of the Eu ions in all configurations is approximately 6.9, very close the spin number of free Eu atoms which indicates the infinitesimal hybridization of Eu's f orbitals with other orbitals in the host crystals. According to Figure 2a, b, in stochiometric systems, ZnO:EuZn and ZnO:EuI, there are minor electronic states available at the Fermi level resulting in limited mobile carriers in those systems. However, this amount of carriers is not sufficient to establish carrier-mediated magnetism in the stochiometric ZnO:Eu systems, and these systems remain paramagnetic [24]. By introducing VO, in the ZnO:EuZn + VO system, the VO's impurity states appear below Eu's 4f states as shown in Figure 2c. Thus, VO does not enhance the carrier concentration in the ZnO:EuZn + VO system either. As shown in Figure 2d in the ZnO:EuZn + ZnI system, ZnI's 4s states appear in a small peak at the Fermi level, partially hybridizing with Eu's 4f states and introducing further carriers at the Fermi level. To investigate the possibility of ferromagnetic coupling in the defective systems, two substitutional Eu ions were located in the supercells. Then the Ef of each system was calculated once for ferromagnetic magnetic alignment (EFM) and once again for antiferromagnetic magnetic alignment (EAFM) of the Eu ions. Finally, ΔE is defined to be EAFM - EFM which is an indicator of ferromagnetic phase stabilization. For Eu ions separated by approximately 3.4 Å (nearest possible distance), ΔE was found to be 21 meV for the ZnO:Eu + ZnI system and 3 meV for the ZnO:Eu + VO system. However, for both systems, the ΔE vanishes when the separation between the Eu ions increases to approximately 6 Å. This trend in ΔE indicates that ZnI induces short range ferromagnetic coupling in the ZnO:Eu system.

Bottom Line: The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated.The total and partial densities of electron states were also determined for both systems.It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. sean.li@unsw.edu.au.

ABSTRACT
Doping ZnO with rare earth and 4d transition elements is a popular technique to manipulate the optical properties of ZnO systems. These systems may also possess intrinsic ferromagnetism due to their magnetic moment borne on 4f and 4d electrons. In this work, the structural, electronic, and magnetic properties of Eu- and Pd-doped ZnO were investigated by the ab initio density functional theory methods based on generalized gradient approximation. The relative stability of incorporation sites of the doped elements in the ZnO host lattice was studied. The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated. The total and partial densities of electron states were also determined for both systems. It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx.

No MeSH data available.


Related in: MedlinePlus