Magnetic interactions in transition-metal-doped ZnO: An<i>ab initio</i>study

Gopal, Priya; Spaldin, Nicola A.

doi:10.1103/physrevb.74.094418

Cited by 303 publications

(187 citation statements)

References 64 publications

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“…Our results are in good agreement with previous LSDA and LSDA+ U studies of Co-doped ZnO. 16 The importance of a correct description of the electronic structure for the determination of the magnetic properties has been emphasized in other recent studies. 24,25 In addition, these studies suggest that the weak antiferromagnetic coupling observed in the undoped Co:ZnO could be turned to a ferromagnetic coupling by electron doping, the stabilization of the FM state being due to the partial occupation of the t 2 -like minority bands.…”

Section: A Structural and Magnetic Propertiessupporting

confidence: 82%

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Microscopic picture of Co clustering in ZnO

et al. 2009

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Density functional theory was applied to study the chemical and magnetic interactions between Co atoms doped in ZnO. It was found that the Co impurities tend to form nanoclusters and the interactions between these atoms are antiferromagnetic within the local spin-density approximation ͑LSDA͒ + Hubbard U approach. The extracted interatomic exchange parameters agree reasonably well with recent experimental results. We have analyzed and compared the electronic structure obtained using the LSDA and LSDA+ U approaches and found that the LSDA+ U gives the most reasonable result, highlighting the importance of short-ranged antiferromagnetic interactions due to superexchange.

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Section: A Structural and Magnetic Propertiessupporting

confidence: 82%

“…15 Similar values have been used in other theoretical calculations on these compounds following the LSDA+ U approach. 16 The wave functions were expanded in a plane-wave basis set with the kineticenergy cutoff of 500 eV. The wurtzite lattice constants were set to a = 3.25 Å and c = 5.21 Å.…”

Section: Computational Detailsmentioning

confidence: 99%

Microscopic picture of Co clustering in ZnO

et al. 2009

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“…In a wide gap semiconductor such as ZnO (E g 3:4 eV), this would place the minority spin Co t 2d states within the band gap, as has been reported from both optical and magnetic measurements for ZnO:Co [13][14][15]. Surprisingly, this is not the case in previous theoretical studies [5][6][7][8].From consideration of Co 3d band coupling, FM interactions between occupied majority t 2d states results in no net energy gain due to filled bonding and antibonding combinations, while AFM interactions can result in a small energy gain (Fig. 1).…”

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confidence: 45%

Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO

2008

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Substitutional cobalt in ZnO has a weak preference for antiferromagnetic ordering. Stabilization of ferromagnetism is achieved through n-type doping, which can be understood through a band coupling model. However, the description of the transition to a ferromagnetic ground state varies within different levels of band theory; issues arise due to the density functional theory underestimation of the band gap of ZnO, and the relative position of the nominally unfilled Co t 2d states. We examine these limitations, including approaches to overcome them, and explain the contradictions in previous studies, which drastically overestimate the doping threshold for magnetic ordering. DOI: 10.1103/PhysRevLett.100.256401 PACS numbers: 71.20.Nr, 71.15.Mb, 75.10.ÿb, 75.50.Pp The potential to simultaneously tune both charge and spin in solid state materials has lead to great interest in the field of spintronics [1]. The ultimate aim is a controllable room temperature semiconducting ferromagnet, which could be used in magnetoelectric and magnetotransport devices. Intrinsically magnetic semiconductors generally possess relatively low Curie temperatures (T C ); however, it has been proposed that incorporating transition metal or rare earth ions into a nonmagnetic semiconductor host lattice, forming a dilute magnetic semiconductor (DMS), may help raise T C above room temperature [2,3].In DMS materials, magnetism is influenced and controlled by the presence of charge carriers in the form of holes (GaAs:Mn) or electrons (GaN:Gd). There is still great debate over the fundamental mechanism behind the origin of the observed high temperature magnetic alignment in many of these systems. The situation is not helped by large variation in both experimental and theoretical studies [4 -8].Cobalt doped ZnO has become a focus of attention due to its reported high T C of up to 700 K and, most promisingly, the reversible cycling of FM ordering [9]. Coupled with existing optical and electrical properties of ZnO, the addition of controllable magnetism could make it a technologically essential material. It has been reported that at Co concentrations of less than 10%, the solubility is good and Co occupies a substitutional Zn site in a 2 charge state [9,10]. B . The splitting between filled e d and empty minority t 2d states for tetrahedral Co is typically on the order of 1.5-2 eV [12]. In a wide gap semiconductor such as ZnO (E g 3:4 eV), this would place the minority spin Co t 2d states within the band gap, as has been reported from both optical and magnetic measurements for ZnO:Co [13][14][15]. Surprisingly, this is not the case in previous theoretical studies [5][6][7][8].From consideration of Co 3d band coupling, FM interactions between occupied majority t 2d states results in no net energy gain due to filled bonding and antibonding combinations, while AFM interactions can result in a small energy gain (Fig. 1). Partial occupation of the empty minority t 2d states will result in a transition to FM ordering through the energy gained from the fi...

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“…The further-neighbor interactions are antiferromagnetic for the electron-doped system ͑with oxygen vacancy͒, suggesting a lower probability for the electron-doped system to be a ferromagnet in agreement with the recent LDA+ U calculations. 73 On the other hand, the further- neighbor interactions for the hole-doped system with a Zn vacancy is ferromagnetic but are much weaker in comparison to the nearest-neighbor interactions. Such short-range exchange interaction indicates the formation of Fe clusters and the possibility of intrinsic ferromagnetism in Fe-doped ZnO to be driven by percolation.…”

Section: Fe-doped Zno With Defectsmentioning

confidence: 99%

“…If the Coulomb correlations are included, as in the LSDA+ U method, the half-filled e↑ band will split and the system will be an insulator. In fact, a recent LSDA+ U calculation 73 indicated an insulating antiferromagnetic state to be more stable in comparison to the ferromagnetic state. Hence, from the preceding discussion we conclude that Fe-doped ZnO is unlikely to stabilize in a ferromagnetic state.…”

Section: Fe-doped Znomentioning

confidence: 99%

Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory

et al. 2007

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Fe-doped ZnO nanocrystals are successfully synthesized and structurally characterized by using x-ray diffraction and transmission electron microscopy. Magnetization measurements on the same system reveal a ferromagnetic to paramagnetic transition temperature above 450 K with a low-temperature transition from the ferromagnetic to the spin-glass state due to canting of the disordered surface spins in the nanoparticle system. Local magnetic probes like electron paramagnetic resonance and Mössbauer spectroscopy indicate the presence of Fe in both valence states Fe 2+ and Fe 3+ . We argue that the presence of Fe 3+ is due to possible hole doping in the system by cation ͑Zn͒ vacancies. In a subsequent ab initio electronic structure calculation, the effects of defects ͑e.g., O and Zn vacancies͒ on the nature and origin of ferromagnetism are investigated for the Fe-doped ZnO system. Electronic structure calculations suggest hole doping ͑Zn vacancy͒ to be more effective to stabilize ferromagnetism in Fe-doped ZnO and our results are consistent with the experimental signature of hole doping in ferromagnetic Fe-doped ZnO samples.

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Magnetic interactions in transition-metal-doped ZnO: Anab initiostudy

Cited by 303 publications

References 64 publications

Microscopic picture of Co clustering in ZnO

Microscopic picture of Co clustering in ZnO

Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO

Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory

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