Elfimov and Galvão Reply:

Elfimov, A. G.; Galvão, R. M. O.

doi:10.1103/physrevlett.85.2409

Cited by 36 publications

(49 citation statements)

References 4 publications

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“…3,18 Most DIM studies, both experimental [10][11][12][13] and theoretical, 12,[19][20][21] suggested that the origin of the observed FM in these oxides is related to cation vacancies or even nitrogen doping in MgO. [22][23][24] Recent theoretical work discussed interdefect coupling mechanisms, 9,25-27 such as high carrier mobility near interfaces. Very recently, Zunger and coworkers 28,29 and Droghetti et al 2 drew attention to the Achilles' heel of all DFT calculations performed with local approximations of the exchange correlation potentials, such as the local spin density approximation and the generalized gradient approximation.…”

Section: -13mentioning

confidence: 99%

Defect-induced magnetism in chemically synthesized nanoscale sheets of MgO

Maoz¹,

Tirosh²,

Bar‐Sadan³

et al. 2011

Phys. Rev. B

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Highly defective MgO nanosheets were prepared by a colloidal synthesis and exhibited low-temperature ferromagnetism which was significantly larger that the magnetization potentially obtainable from the low transition-metal impurity concentration. Electron paramagnetic resonance experiments confirmed that the magnetization did not significantly involve impurities and that the nanosheets consisted of strongly interacting spin clusters which disappeared upon high-temperature annealing. These spins were concentrated along extended defects, possibly as unpaired electrons trapped at oxygen vacancies. DIM should be highly sensitive to the various defect or impurity characteristics, posing experimental and theoretical difficulties that demand prudence. Experimentally, Abraham et al.14 and Garcia et al. 15 showed the ease with which a ferromagnetic signal is obtained in such oxides due to impurities. The problem of paramagnetic transition-metal ion impurities as a source of magnetism was recently comprehensively studied by Khalid et al. 16 Much of the previous experimental work claiming to have detected DIM in MgO 9-13 as well as other materials ignored the need to precisely determine the paramagnetic metal impurity concentration in the analysis of results. Preparation of samples by deposition in a stainlesssteel apparatus, 12 using characterization techniques such as x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) with insufficient sensitivity to low concentrations of impurities, 9,13 or using less-than ultrapure precursors or not addressing precursor purity 10,11 may lead to confusion about the source of the observed ferromagnetism. The theory of DIM is also problematic: In the early 70s large magnetic moments were predicted on neighboring oxygen atoms due to Mg vacancies.17 Elfimov et al. 3 predicted cation vacancy-induced ferromagnetism using density functional theory (DFT) calculations. Also, further theoretical work attributed the formation of magnetic moments and the resulting FM to spin-polarized holes residing on cation p orbitals either at vacancy or impurity sites. 3,18 Most DIM studies, both experimental [10][11][12][13] and theoretical, 12,[19][20][21] suggested that the origin of the observed FM in these oxides is related to cation vacancies or even nitrogen doping in MgO.22-24 Recent theoretical work discussed interdefect coupling mechanisms, 9,25-27 such as high carrier mobility near interfaces. Very recently, Zunger and coworkers 28,29 and Droghetti et al. 2 drew attention to the Achilles' heel of all DFT calculations performed with local approximations of the exchange correlation potentials, such as the local spin density approximation and the generalized gradient approximation. These methods overestimate spin density delocalization, leading to a half-metallic ground state with a relatively strong interdefect ferromagnetic interaction.In this paper we present results obtained on highly defective MgO nanosheets (MgO-NSs) prepared by a colloidal synthesis from the ultrapure precurso...

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Section: -13mentioning

confidence: 99%

Defect-induced magnetism in chemically synthesized nanoscale sheets of MgO

Maoz¹,

Tirosh²,

Bar‐Sadan³

et al. 2011

Phys. Rev. B

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“…Due to residual selfinteraction [12], the energy splitting between occupied and unoccupied states is generally underestimated in approximate DFT functionals like LDA or GGA. This is particularly true for atomic d-and f-orbitals, but also for the p-orbitals of anionic first-row elements like O or N, which are sometimes described as "strongly correlated" systems [6]. The key for the correct placement of unoccupied states relative to the spectrum of occupied states lies in the observation that LDA/GGA and HF-theory produce errors of opposite sign in the energy E between adjacent integer occupation numbers n i of the highest occupied state i [13,14]: As illustrated schematically in Fig.…”

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confidence: 99%

“…2a) for the stabilization of the polaronic state is exceeded. Thus, properties like the lattice distortion, hyperfine parameters [4], or magnetic interactions [5,6] can generally be expected to be relatively insensitive to the question how well the condition eq. (3) is fulfilled, if only the applied method stabilizes the polaronic state.…”

mentioning

confidence: 99%

“…delocalization among equivalent sites, bears great importance for physical phenomena like hyperfine interactions [4], magnetism without d-elements [5,6], and p-type doping in wide-gap oxides [7,8].…”

mentioning

confidence: 99%

“…A number of electronic structure methods are able to restore the qualitative picture of single-site localization, e.g., self-interaction correction (SIC) [4,5], DFT+U [6,9], and hybrid-DFT [10,11].…”

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confidence: 99%

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Polaronic hole localization and multiple hole binding of acceptors in oxide wide-gap semiconductors

2009

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Acceptor-bound holes in oxides often localize asymmetrically at one out of several equivalent oxygen ligands. Whereas Hartree-Fock (HF) theory overly favors such symmetry-broken polaronic holelocalization in oxides, standard local density (LD) calculations suffer from spurious delocalization among several oxygen sites. These opposite biases originate from the opposite curvatures of the energy as a function of the fractional occupation number n, i.e., < 0 in HF and > 0 in LD. We recover the correct linear behavior, = 0, that removes the (de)localization bias by formulating a

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Collisionless Damping of Geodesic Acoustic Mode in a Multi‐Ion Plasma with Superthermal Ions

Liu

2015

Contrib. Plasma Phys.

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The dispersion relation of geodesic acoustic mode is investigated in a multi-ion toroidal plasma on the basis of linear gyrokinetic equations where ions are assumed to take a nonextensive distribution. It is found that the frequency of GAM becomes larger with the decrease of q. Consequently, GAM will damp more rapidly. The effective charge corresponding to the maximum damping rate is found to move towards unity as q decreases. As indicates that in a plasma with superthermal bulk ions, the influence of the impurity ion on the damping rate is weakened.

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Elfimov and Galvão Reply:

Cited by 36 publications

References 4 publications

Defect-induced magnetism in chemically synthesized nanoscale sheets of MgO

Defect-induced magnetism in chemically synthesized nanoscale sheets of MgO

Polaronic hole localization and multiple hole binding of acceptors in oxide wide-gap semiconductors

Collisionless Damping of Geodesic Acoustic Mode in a Multi‐Ion Plasma with Superthermal Ions

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