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Electronic structure and magnetism in Ni0.0625Zn0.9375O : An ab initio study
ARTICLE IN PRESS Journal of Magnetism and Magnetic Materials 321 (2009) 2547–2549
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Electronic structure and magnetism in Ni0:0625 Zn0:9375 O: An ab initio study Rafael Gonza´lez Herna´ndez a,b,, William Lo´pez Pe´rez a, M. Jairo Arbey Rodrı´guez b,1 a b
GFMC, Departamento de Fı´sica, Universidad del Norte, A. A. 1569, Barranquilla, Colombia ´,Colombia GEMA, Departamento de Fı´sica, Universidad Nacional de Colombia, A. A. 5997, Bogota
a r t i c l e in fo
abstract
Article history: Received 22 December 2008 Received in revised form 16 February 2009 Available online 26 March 2009
We carry out first principles spin polarized calculations in order to study the electronic structure and magnetism of Ni0:0625 Zn0:9375 O compound using density functional theory (DFT) within a plane-wave ultrasoft pseudopotential scheme. The electronic properties of Nix Zn1x O at a concentration of 6.25% are analyzed using a 2 2 2 wurtzite ZnO supercell. We optimize the lattice constants of ZnO pure and Ni0:0625 Zn0:9375 O. We observe that if one Zn atom is substituted by one Ni atom in the wurtzite ZnO supercell, the lattice parameters decrease slightly some thousandths of angstrom. We also find a stable ferromagnetic state in Ni doped ZnO with a total magnetization of 2:04 mB per supercell. Using the optimized lattice parameters, we have calculated the band structure and density of states of Ni0:0625 Zn0:9375 O. Published by Elsevier B.V.
PACS: 71.15.Mb 74.25.Jb 75.50.Pp Keywords: DFT Electronic property Magnetic semiconductor
1. Introduction The possibility to manipulate the spin of the electron, as well as the charge, opens up fascinating routes for processing information and data storage. This is particularly exciting in terms of semiconductor spintronics, where conventional chargebased electronics could be replaced with devices possessing both spin and charge functionality. Dilute magnetic semiconductors (DMS)—semiconductors doped with a few percent of magnetic atoms—are being actively investigated in the development of spintronic devices. While there has been much work on the III–V DMS materials, notably (In,Mn)As and (Ga,Mn)As, their ferromagnetic Curie temperatures ðT c Þ (90 K for (In,Mn)As [1] and 172 K for (Ga,Mn)As [2]) are too low for practical applications. The realization of practical commercial or mobile devices will require the development of semiconductors that can retain their ferromagnetic magnetic properties above room temperature. As a result, significant research effort has been focused on developing alternative DMS materials with higher Curie temperatures [3]. ZnO is also highly relevant from an application perspective as the material is piezoelectric, optically transparent, and has a large band gap of 3.4 eV. The motivation for studying semiconducting oxides, particularly ZnO [4], for spintronics was stimulated by the
Corresponding author.
E-mail addresses: [email protected] (R.G. Herna´ndez), jarodriguezm@ unal.edu.co (M. Jairo Arbey Rodrı´guez). 1 Tel.: +57 1 3165000; fax: +57 1 3165135. 0304-8853/$ - see front matter Published by Elsevier B.V. doi:10.1016/j.jmmm.2009.03.037
work of Dietl et al. [5]. Dietl predicted that Mn doped ZnO would have a Curie temperature above room temperature. The theory is based on an indirect exchange mechanism where the ferromagnetism between magnetic dopants is mediated by holes in the valence band. Dietl’s theory has proven useful in understanding the experimental results for (Ga,Mn)As. However, it does not appear to be consistent with the experimental results for transition metal doped wide band gap semiconductors, such as ZnO. It has generated multiple experimental and computational studies of transition metal doping in ZnO [6]. Sato and KatayamaYoshida [7] considered ZnO doped with Mn, Fe, Co and Ni. The calculations were performed with the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA) method assuming random distribution of the 3d substitutional impurities on the Zn sites. The comparison of the total energies of the ferromagnetic and so-called disordered-local-moment (DLM) states showed, that the ferromagnetism is stable for Fe, Co and Ni impurities and unstable for Mn impurity. Recently, Radovan and Gamelin [8] reported high-T c ferromagnetism in nanocrystalline ZnO:Ni prepared from solution at low temperatures. The appearance of ferromagnetism upon room-temperature aggregation of paramagnetic ZnO:Ni DMS nanocrystals unambiguously demonstrates its intrinsic origin and additionally represents a significant advance toward chemically controlled spin effects in semiconductor nanostructures. From the viewpoint of technological application, a detailed study on the feasibility of ferromagnetic Ni doped ZnO is relevant. Therefore, in this work we have studied the electronic and magnetic properties of Ni0:0625 Zn0:9375 O using first principles plane wave calculations.
ARTICLE IN PRESS 2548
´ndez et al. / Journal of Magnetism and Magnetic Materials 321 (2009) 2547–2549 R.G. Herna
2. Computational detail The total energy and electronic structure calculations were performed using the first principle pseudopotential method within spin density functional theory. We have employed the atomic ultrasoft pseudopotentials [9] and the generalized gradient approximation (GGA) given by Perdew et al. [10] for the exchange and correlation potential. The calculations were performed using Quantum-ESPRESSO package [11]. The electron wave functions were expanded in plane waves up to a cutoff energy of 35 Ry, and a gamma centered 5 5 5 k mesh was used to sample the irreducible Brillouin zone in the Monkhorst–Pack special scheme [12]. Methfessel–Paxton smearing technique with a smearing width of 0.04 Ry was adopted [13]. These parameters ensure a convergence better than 0.01 meV for the total energy. In order to investigate the magnetism of Nix Zn1x O with x ¼ 0:0625, we have calculated the electronic structure of Ni doped ZnO using 2 2 2 supercell based from conventional ZnO wurtzite unit cell. A Zn atom in the supercell was replaced by a Ni atom to represent a concentration of 6.25%. Experimentally, it has been found that a Mn atom replaces to a Zn atom when Mn atoms are incorporated in the ZnO lattice [14]. By the similarity between the electronic affinity, electronegativity and atomic radius of Ni and Mn atoms, the same behavior would be expected when a Ni atoms are incorporated in the ZnO lattice. Recently, this prediction has been observed by Liu et al. for Nix Zn1x O thin films grown on quartz substrates with the Ni concentrations of 5%, 10% and 20% in the films [15].
Fig. 1. Calculated band structure of the majority spin for Ni0:0625 Zn0:9375 O in GGA approximation. The red line indicates the Fermi energy level, that is carried to zero.
3. Result and discussion ZnO pure structure in the 2 2 2 wurtzite supercell was optimized. The lattice constant and the relation c=a obtained were ˚ and 1.609, respectively, which are in good agreement with 3:293 A ˚ and c=a ¼ 1:602 [16]. These the experimental data a ¼ 3:250 A results confirm the usual trend of GGA approach to overestimate the lattice constants values. The lattice parameters in Ni0:0625 Zn0:9375 O supercell with one Zn atom substituted by one Ni atom, also were optimized. We ˚ obtained slightly more small values than pure ZnO: a ¼ 3:292 A and c=a ¼ 1:604, due to the small difference in atomic radius of the Ni and Zn atoms. Electronic structure of Ni0:0625 Zn0:9375 O was calculated with the optimized structural parameters. We have carried out total energy calculations at a concentration of 12.5% of Ni to confirm the ferromagnetism of the compound; in this case two Zn atoms are substituted by two Ni atoms in the supercell, a ˚ between Ni atoms in the supercell possible separation of 6:22 A was considered. This system shown a stable ferromagnetic state with a total energy of 15.92 meV lower than antiferromagnetic state. A total magnetization of 2:04 mB per supercell was obtained. The calculations are in agreement with recent experimental studies where Ni doped ZnO shows a ferromagnetic behavior to room temperature [17–19]. To investigate the effect of electron correlations, we have repeated the calculation with LDA+U approach [20] and found that ferromagnetic configuration is also the ground state. In this approximation, the calculated value of magnetic moments was 2:00 mB per supercell. The band electronic structures of ferromagnetic Ni0:0625 Zn0:9375 O are shown in the Figs. 1 and 2, for majority and minority spin, respectively. In there figures, the Fermi energy level is adopted as zero of energy. In Fig. 1, some bands belonging to the conduction band of majority spin states appear below the Fermi energy level. These majority spin states do not overlap with those of valence and therefore, maintain a small band gap below the Fermi energy level. So Ni0:0625 Zn0:9375 O is metallic for the majority
Fig. 2. Calculated band structure of the minority spin for Ni0:0625 Zn0:9375 O in GGA approximation. The red line indicates the Fermi energy level, that is carried to zero.
spin component. In Fig. 2, the non-existence of a energy gap around Fermi energy level is observed. Around Fermi energy level some bands of the 3d-Ni and 2p-O orbital are localized, indicating a metallic behavior of the Ni0:0625 Zn0:9375 O in the minority spin orientation. Total and partial density of states as function of energy for Ni0:0625 Zn0:9375 O are shown in Fig. 3. We observe that the ferromagnetic system have metallic behavior in both spin orientation. In the majority spin polarization, total DOS presents a region below 1 eV and mainly due to 3d-Zn electrons with some small contribution of the 2p-O, 3d-Ni and 4s-Zn orbital. A occupation of the 3d-Zn states around Fermi energy level is presented, disappearing the existing gap in the bulk ZnO. The curve of the 3d-Ni states has a high peak at 2 eV below the Fermi energy level, indicating localized orbital. A similar result for 3d-Ni state energy have been found by Yin et al. [21] by valence band PES measurements. In the minority spin orientation, total DOS shows a similar states contribution below the Fermi energy level to presented in the majority spin orientation. We observe that the 2p-O and 3d-Ni states present a considerable hybridization around the Fermi energy level with a similar shape of the partial DOS in the same energy window. This fact reveal an atomic hybridization between the nickel atom and its four neighboring oxygen, this provides
ARTICLE IN PRESS ´ndez et al. / Journal of Magnetism and Magnetic Materials 321 (2009) 2547–2549 R.G. Herna
2549
(DFT) within a plane-wave scheme. We found a significant magnetization of Ni doped ZnO system. When Zn atoms are substituted by Ni atoms in ZnO semiconductor, the nickel spin polarization magnetizes p electrons of neighboring oxygen by means of the p–d hybridization mechanism. Electronic structure of Ni0:0625 Zn0:9375 O is sensitive to the spin orientation, related to the state contribution around the Fermi energy level. Our results making this material an important candidate in the design of new functional devices for spintronic applications, using the negative electronic affinity in ZnO. Acknowledgments We thank to Universidad del Norte and DIB-Universidad Nacional de Colombia for their financial support during the realization of this work. The calculations were carried out in the Hiperlab cluster of basic sciences in Universidad del Norte, Barranquilla. References
Fig. 3. Calculated total and partial density of states for Ni0:0625 Zn0:9375 O in GGA approximation. The dotted line indicates the Fermi energy level, that is carried to zero.
magnetization to the nickel atom and to the neighboring oxygen atoms. Therefore, this type of p–d hybridization could establish the ferromagnetic character in Ni0:0625 Zn0:9375 O. From the partial DOS of the 3d-Ni, it can be seen the curve has two peaks pronounced, an around the Fermi energy level and another at 1:5 eV below the Fermi energy level, indicating localized 3d-Ni orbitals, in agree with Yin et al. results [21]. On the other hand, the calculated electronic structure within LDA þ U approach shows a half-metallic behavior, and the d-Ni states also hybridize strongly with the p-O states like in GGA approximation. This p–d hybridization produces a long range ferromagnetic coupling among all Ni dopants in the ZnO semiconductor. A similar electronic behavior was found by et al. for Cu-doped ZnO [22].
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
4. Conclusions In this work, the electronic and magnetic properties of Ni0:0625 Zn0:9375 O were studied using density functional theory
T. Schallenberg, H. Munekata, Appl. Phys. Lett. 89 (2006) 042507. A.M. Nazmul, S. Sugahara, M. Tanaka, Phys. Rev. B 67 (2003) 241308. S.A. Chambers, Surf. Sci. Rep. 61 (2006) 345. M. Ivill, M.E. Overberg, C.R. Abernathy, D.P. Norton, A.F. Hebard, N. Theodoropoulou, J.D. Budai, Solid State Electron. 47 (2003) 2215. T. Dietl, H. Ohno, F. Matsukura, J. Cibert, D. Ferrand, Science 287 (2000) 1019. C. Liu, F. Yun, H. Morko, J. Mater. Sci. Mater. Electron. 16 (2005) 555. K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys. Part. 2 40 (2001) L334. V. Pavle, V. Radovan, R. Gamelin Daniel, Phys. Rev. Lett. 91 (2003) 157202. K. Laasonen, A. Pasquarello, R. Car, C. Lee, D. Vanderbilt, Phys. Rev. B 47 (1993) 10142. J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865. S. Baroni, A. dal Corso, S. de Gironcoli, P. Giannozzi, C. Cavazzoni, et al. hhttp:// www.pwscf.org/i. H.J. Monkhorst, J.D. Pack, Phys. Rev. B 13 (1976) 5188. M. Methfessel, A.T. Paxon, Phys. Rev. B 40 (1989) 3616. V.K. Sharma, R. Xalxo, G.D. Varma, Cryst. Res. Technol. 42 (2007) 34. E. Liu, P. Xiao, J.S. Chen, B.C. Lim, L. Li, Curr. Appl. Phys. 8 (2008) 408. E. Kisi, M.M. Elcombe, Cryst. Struct. Commun. C 45 (1989) 1867. C.J. Cong, J.H. Hong, Q.Y. Liu, L. Liao, K.L. Zhang, Solid State Commun. 138 (2006) 511. B.B. Li, X.Q. Xiu, R. Zhang, Z.K. Tao, L. Chen, Z.L. Xie, Y.D. Zheng, Z. Xie, Mater. Sci. Semiconductor Process. 9 (2006) 141. X. Mao, W. Zhong, Y. Du, J. Magn. Magn. Mater. 320 (2008) 1102. V.I. Anisimov, J. Zaanen, O.K. Andersen, Phys. Rev. B 44 (1991) 943. Z. Yin, N. Chen, F. Yang, S. Song, C. Chai, J. Zhong, H. Qian, K. Ibrahim, Solid State Commun. 135 (2005) 430. L.-H. Ye, A.J. Freeman, B. Delley, Phys. Rev. B 73 (2006) 033203.
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Electronic structure and magnetism in Ni0:0625 Zn0:9375 O: An ab initio study Rafael Gonza´lez Herna´ndez a,b,, William Lo´pez Pe´rez a, M. Jairo Arbey Rodrı´guez b,1 a b
GFMC, Departamento de Fı´sica, Universidad del Norte, A. A. 1569, Barranquilla, Colombia ´,Colombia GEMA, Departamento de Fı´sica, Universidad Nacional de Colombia, A. A. 5997, Bogota
a r t i c l e in fo
abstract
Article history: Received 22 December 2008 Received in revised form 16 February 2009 Available online 26 March 2009
We carry out first principles spin polarized calculations in order to study the electronic structure and magnetism of Ni0:0625 Zn0:9375 O compound using density functional theory (DFT) within a plane-wave ultrasoft pseudopotential scheme. The electronic properties of Nix Zn1x O at a concentration of 6.25% are analyzed using a 2 2 2 wurtzite ZnO supercell. We optimize the lattice constants of ZnO pure and Ni0:0625 Zn0:9375 O. We observe that if one Zn atom is substituted by one Ni atom in the wurtzite ZnO supercell, the lattice parameters decrease slightly some thousandths of angstrom. We also find a stable ferromagnetic state in Ni doped ZnO with a total magnetization of 2:04 mB per supercell. Using the optimized lattice parameters, we have calculated the band structure and density of states of Ni0:0625 Zn0:9375 O. Published by Elsevier B.V.
PACS: 71.15.Mb 74.25.Jb 75.50.Pp Keywords: DFT Electronic property Magnetic semiconductor
1. Introduction The possibility to manipulate the spin of the electron, as well as the charge, opens up fascinating routes for processing information and data storage. This is particularly exciting in terms of semiconductor spintronics, where conventional chargebased electronics could be replaced with devices possessing both spin and charge functionality. Dilute magnetic semiconductors (DMS)—semiconductors doped with a few percent of magnetic atoms—are being actively investigated in the development of spintronic devices. While there has been much work on the III–V DMS materials, notably (In,Mn)As and (Ga,Mn)As, their ferromagnetic Curie temperatures ðT c Þ (90 K for (In,Mn)As [1] and 172 K for (Ga,Mn)As [2]) are too low for practical applications. The realization of practical commercial or mobile devices will require the development of semiconductors that can retain their ferromagnetic magnetic properties above room temperature. As a result, significant research effort has been focused on developing alternative DMS materials with higher Curie temperatures [3]. ZnO is also highly relevant from an application perspective as the material is piezoelectric, optically transparent, and has a large band gap of 3.4 eV. The motivation for studying semiconducting oxides, particularly ZnO [4], for spintronics was stimulated by the
Corresponding author.
E-mail addresses: [email protected] (R.G. Herna´ndez), jarodriguezm@ unal.edu.co (M. Jairo Arbey Rodrı´guez). 1 Tel.: +57 1 3165000; fax: +57 1 3165135. 0304-8853/$ - see front matter Published by Elsevier B.V. doi:10.1016/j.jmmm.2009.03.037
work of Dietl et al. [5]. Dietl predicted that Mn doped ZnO would have a Curie temperature above room temperature. The theory is based on an indirect exchange mechanism where the ferromagnetism between magnetic dopants is mediated by holes in the valence band. Dietl’s theory has proven useful in understanding the experimental results for (Ga,Mn)As. However, it does not appear to be consistent with the experimental results for transition metal doped wide band gap semiconductors, such as ZnO. It has generated multiple experimental and computational studies of transition metal doping in ZnO [6]. Sato and KatayamaYoshida [7] considered ZnO doped with Mn, Fe, Co and Ni. The calculations were performed with the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA) method assuming random distribution of the 3d substitutional impurities on the Zn sites. The comparison of the total energies of the ferromagnetic and so-called disordered-local-moment (DLM) states showed, that the ferromagnetism is stable for Fe, Co and Ni impurities and unstable for Mn impurity. Recently, Radovan and Gamelin [8] reported high-T c ferromagnetism in nanocrystalline ZnO:Ni prepared from solution at low temperatures. The appearance of ferromagnetism upon room-temperature aggregation of paramagnetic ZnO:Ni DMS nanocrystals unambiguously demonstrates its intrinsic origin and additionally represents a significant advance toward chemically controlled spin effects in semiconductor nanostructures. From the viewpoint of technological application, a detailed study on the feasibility of ferromagnetic Ni doped ZnO is relevant. Therefore, in this work we have studied the electronic and magnetic properties of Ni0:0625 Zn0:9375 O using first principles plane wave calculations.
ARTICLE IN PRESS 2548
´ndez et al. / Journal of Magnetism and Magnetic Materials 321 (2009) 2547–2549 R.G. Herna
2. Computational detail The total energy and electronic structure calculations were performed using the first principle pseudopotential method within spin density functional theory. We have employed the atomic ultrasoft pseudopotentials [9] and the generalized gradient approximation (GGA) given by Perdew et al. [10] for the exchange and correlation potential. The calculations were performed using Quantum-ESPRESSO package [11]. The electron wave functions were expanded in plane waves up to a cutoff energy of 35 Ry, and a gamma centered 5 5 5 k mesh was used to sample the irreducible Brillouin zone in the Monkhorst–Pack special scheme [12]. Methfessel–Paxton smearing technique with a smearing width of 0.04 Ry was adopted [13]. These parameters ensure a convergence better than 0.01 meV for the total energy. In order to investigate the magnetism of Nix Zn1x O with x ¼ 0:0625, we have calculated the electronic structure of Ni doped ZnO using 2 2 2 supercell based from conventional ZnO wurtzite unit cell. A Zn atom in the supercell was replaced by a Ni atom to represent a concentration of 6.25%. Experimentally, it has been found that a Mn atom replaces to a Zn atom when Mn atoms are incorporated in the ZnO lattice [14]. By the similarity between the electronic affinity, electronegativity and atomic radius of Ni and Mn atoms, the same behavior would be expected when a Ni atoms are incorporated in the ZnO lattice. Recently, this prediction has been observed by Liu et al. for Nix Zn1x O thin films grown on quartz substrates with the Ni concentrations of 5%, 10% and 20% in the films [15].
Fig. 1. Calculated band structure of the majority spin for Ni0:0625 Zn0:9375 O in GGA approximation. The red line indicates the Fermi energy level, that is carried to zero.
3. Result and discussion ZnO pure structure in the 2 2 2 wurtzite supercell was optimized. The lattice constant and the relation c=a obtained were ˚ and 1.609, respectively, which are in good agreement with 3:293 A ˚ and c=a ¼ 1:602 [16]. These the experimental data a ¼ 3:250 A results confirm the usual trend of GGA approach to overestimate the lattice constants values. The lattice parameters in Ni0:0625 Zn0:9375 O supercell with one Zn atom substituted by one Ni atom, also were optimized. We ˚ obtained slightly more small values than pure ZnO: a ¼ 3:292 A and c=a ¼ 1:604, due to the small difference in atomic radius of the Ni and Zn atoms. Electronic structure of Ni0:0625 Zn0:9375 O was calculated with the optimized structural parameters. We have carried out total energy calculations at a concentration of 12.5% of Ni to confirm the ferromagnetism of the compound; in this case two Zn atoms are substituted by two Ni atoms in the supercell, a ˚ between Ni atoms in the supercell possible separation of 6:22 A was considered. This system shown a stable ferromagnetic state with a total energy of 15.92 meV lower than antiferromagnetic state. A total magnetization of 2:04 mB per supercell was obtained. The calculations are in agreement with recent experimental studies where Ni doped ZnO shows a ferromagnetic behavior to room temperature [17–19]. To investigate the effect of electron correlations, we have repeated the calculation with LDA+U approach [20] and found that ferromagnetic configuration is also the ground state. In this approximation, the calculated value of magnetic moments was 2:00 mB per supercell. The band electronic structures of ferromagnetic Ni0:0625 Zn0:9375 O are shown in the Figs. 1 and 2, for majority and minority spin, respectively. In there figures, the Fermi energy level is adopted as zero of energy. In Fig. 1, some bands belonging to the conduction band of majority spin states appear below the Fermi energy level. These majority spin states do not overlap with those of valence and therefore, maintain a small band gap below the Fermi energy level. So Ni0:0625 Zn0:9375 O is metallic for the majority
Fig. 2. Calculated band structure of the minority spin for Ni0:0625 Zn0:9375 O in GGA approximation. The red line indicates the Fermi energy level, that is carried to zero.
spin component. In Fig. 2, the non-existence of a energy gap around Fermi energy level is observed. Around Fermi energy level some bands of the 3d-Ni and 2p-O orbital are localized, indicating a metallic behavior of the Ni0:0625 Zn0:9375 O in the minority spin orientation. Total and partial density of states as function of energy for Ni0:0625 Zn0:9375 O are shown in Fig. 3. We observe that the ferromagnetic system have metallic behavior in both spin orientation. In the majority spin polarization, total DOS presents a region below 1 eV and mainly due to 3d-Zn electrons with some small contribution of the 2p-O, 3d-Ni and 4s-Zn orbital. A occupation of the 3d-Zn states around Fermi energy level is presented, disappearing the existing gap in the bulk ZnO. The curve of the 3d-Ni states has a high peak at 2 eV below the Fermi energy level, indicating localized orbital. A similar result for 3d-Ni state energy have been found by Yin et al. [21] by valence band PES measurements. In the minority spin orientation, total DOS shows a similar states contribution below the Fermi energy level to presented in the majority spin orientation. We observe that the 2p-O and 3d-Ni states present a considerable hybridization around the Fermi energy level with a similar shape of the partial DOS in the same energy window. This fact reveal an atomic hybridization between the nickel atom and its four neighboring oxygen, this provides
ARTICLE IN PRESS ´ndez et al. / Journal of Magnetism and Magnetic Materials 321 (2009) 2547–2549 R.G. Herna
2549
(DFT) within a plane-wave scheme. We found a significant magnetization of Ni doped ZnO system. When Zn atoms are substituted by Ni atoms in ZnO semiconductor, the nickel spin polarization magnetizes p electrons of neighboring oxygen by means of the p–d hybridization mechanism. Electronic structure of Ni0:0625 Zn0:9375 O is sensitive to the spin orientation, related to the state contribution around the Fermi energy level. Our results making this material an important candidate in the design of new functional devices for spintronic applications, using the negative electronic affinity in ZnO. Acknowledgments We thank to Universidad del Norte and DIB-Universidad Nacional de Colombia for their financial support during the realization of this work. The calculations were carried out in the Hiperlab cluster of basic sciences in Universidad del Norte, Barranquilla. References
Fig. 3. Calculated total and partial density of states for Ni0:0625 Zn0:9375 O in GGA approximation. The dotted line indicates the Fermi energy level, that is carried to zero.
magnetization to the nickel atom and to the neighboring oxygen atoms. Therefore, this type of p–d hybridization could establish the ferromagnetic character in Ni0:0625 Zn0:9375 O. From the partial DOS of the 3d-Ni, it can be seen the curve has two peaks pronounced, an around the Fermi energy level and another at 1:5 eV below the Fermi energy level, indicating localized 3d-Ni orbitals, in agree with Yin et al. results [21]. On the other hand, the calculated electronic structure within LDA þ U approach shows a half-metallic behavior, and the d-Ni states also hybridize strongly with the p-O states like in GGA approximation. This p–d hybridization produces a long range ferromagnetic coupling among all Ni dopants in the ZnO semiconductor. A similar electronic behavior was found by et al. for Cu-doped ZnO [22].
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
4. Conclusions In this work, the electronic and magnetic properties of Ni0:0625 Zn0:9375 O were studied using density functional theory
T. Schallenberg, H. Munekata, Appl. Phys. Lett. 89 (2006) 042507. A.M. Nazmul, S. Sugahara, M. Tanaka, Phys. Rev. B 67 (2003) 241308. S.A. Chambers, Surf. Sci. Rep. 61 (2006) 345. M. Ivill, M.E. Overberg, C.R. Abernathy, D.P. Norton, A.F. Hebard, N. Theodoropoulou, J.D. Budai, Solid State Electron. 47 (2003) 2215. T. Dietl, H. Ohno, F. Matsukura, J. Cibert, D. Ferrand, Science 287 (2000) 1019. C. Liu, F. Yun, H. Morko, J. Mater. Sci. Mater. Electron. 16 (2005) 555. K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys. Part. 2 40 (2001) L334. V. Pavle, V. Radovan, R. Gamelin Daniel, Phys. Rev. Lett. 91 (2003) 157202. K. Laasonen, A. Pasquarello, R. Car, C. Lee, D. Vanderbilt, Phys. Rev. B 47 (1993) 10142. J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865. S. Baroni, A. dal Corso, S. de Gironcoli, P. Giannozzi, C. Cavazzoni, et al. hhttp:// www.pwscf.org/i. H.J. Monkhorst, J.D. Pack, Phys. Rev. B 13 (1976) 5188. M. Methfessel, A.T. Paxon, Phys. Rev. B 40 (1989) 3616. V.K. Sharma, R. Xalxo, G.D. Varma, Cryst. Res. Technol. 42 (2007) 34. E. Liu, P. Xiao, J.S. Chen, B.C. Lim, L. Li, Curr. Appl. Phys. 8 (2008) 408. E. Kisi, M.M. Elcombe, Cryst. Struct. Commun. C 45 (1989) 1867. C.J. Cong, J.H. Hong, Q.Y. Liu, L. Liao, K.L. Zhang, Solid State Commun. 138 (2006) 511. B.B. Li, X.Q. Xiu, R. Zhang, Z.K. Tao, L. Chen, Z.L. Xie, Y.D. Zheng, Z. Xie, Mater. Sci. Semiconductor Process. 9 (2006) 141. X. Mao, W. Zhong, Y. Du, J. Magn. Magn. Mater. 320 (2008) 1102. V.I. Anisimov, J. Zaanen, O.K. Andersen, Phys. Rev. B 44 (1991) 943. Z. Yin, N. Chen, F. Yang, S. Song, C. Chai, J. Zhong, H. Qian, K. Ibrahim, Solid State Commun. 135 (2005) 430. L.-H. Ye, A.J. Freeman, B. Delley, Phys. Rev. B 73 (2006) 033203.