Lattice dynamics of NiO

Reichardt, W.; Wagner, Veit; Kress, W.

doi:10.1088/0022-3719/8/23/009

Cited by 80 publications

(50 citation statements)

References 20 publications

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“…This is in reasonable agreement with previous reports indicating a single TO excitation with an energy varying between 46 and 50 meV [15,16]. This ZC splitting of approximately 5 meV is larger in absolute magnitude than observed in MnO, (despite the smaller distortion angle), and corresponds to roughly 10% of the average energy of the two modes.…”

Section: Methodssupporting

confidence: 93%

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Role of electronic correlations on the phonon modes of MnO and NiO

et al. 2003

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The possibility of magnetic-order induced phonon anisotropy in single crystals of MnO and NiO is investigated using inelastic neutron scattering. Below TN both compounds exhibit a splitting in their transverse optical phonon spectra of approximately 10%. This behavior illustrates that, contrary to general assumption, the dynamic properties of MnO and NiO are substantially non-cubic.PACS numbers: 75.30.Gw, 78.70.Nx The failure of ab initio approximations to correctly incorporate many-body effects such as electron exchange and correlation is an issue at the core of contemporary solid-state research. Although these effects are important in almost all solids, they are essential for a proper description of co-operative phenomena such as antiferromagnetism, charge-ordering, superconductivity and colossal magnetoresistance.Despite the status of MnO and NiO as benchmark materials for the study of correlated electron systems and frequent use in first principles electronic structure investigations, many aspects of the physics of the 3d transition metal monoxides requires better theoretical explanation. For example, the basic physical properties predicted for MnO and NiO (e.g. band-gaps, distortion angles and phonon spectra) differ radically depending upon which techniques have been employed [1,2].In a recent publication comparing different ab initio and model band-structure models on MnO (including local spin-density approximation (LSDA) and 'LSDA + model' calculations), Massidda et al. [2] suggest that although the electronic density in MnO is approximately cubic, the lowering of symmetry associated with antiferromagnetic ordering can induce an electronic response that is significantly non-cubic. This results in the dynamical properties of the system, such as transverse optical (TO) phonons, exhibiting substantial "magneticorder induced anisotropy".One of the predicted features from such calculations is that the zone center (ZC) optical phonon modes should split depending on their polarization. A higher energy occurs for a mode polarized along the [111] direction and a lower energy for degenerate modes polarized in the orthogonal ferromagnetic plane, see Table I. Massidda et al. [2] find that this effect arises solely due to the magnetic ordering, and would even occur in the absence of any rhombohedral distortion. By comparing results from four different approximation schemes, lower and upper bounds of 3-10% for the magnitude of the splitting are estimated. Variations in the splitting due to the distortion are calculated to be less than 1%.Although similar theoretical calculations have not yet been performed for NiO, the results of measurements of NiO TO phonons are predicted to be qualitatively similar to those in MnO. Indeed, it has been suggested that the splitting in NiO may be even greater in absolute magnitude than in MnO due to the larger magnetic superexchange [3].MnO and NiO are classic examples of type-II antiferromagnets possessing the cubic rock-salt structure. Below T N , exchange-striction causes contra...

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Section: Methodssupporting

confidence: 93%

“…Room temperature TO dispersion curves for the [111] and [001] directions of antiferromagnetically ordered NiO are presented in figure 4(b)(filled round markers). Squares represent the data of Reichardt et al [15], also collected at room temperature.…”

Section: Methodsmentioning

confidence: 99%

Role of electronic correlations on the phonon modes of MnO and NiO

et al. 2003

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“…1, we show the calculated phonon frequencies for MnO and NiO at their theoretical equilibrium geometries together with the measured data. [4][5][6][7][8] Note that for both MnO ͑Refs. 6 and 8͒ and NiO ͑Refs.…”

Section: ͑2͒mentioning

confidence: 99%

“…6 and 8͒ and NiO. 5,7 The specific difficulties [11][12][13][14][15] in predicting the lattice dynamics of Mott-Hubbard insulators are: ͑i͒ the highly correlated nature of electronic states in these materials and ͑ii͒ the slight lowering of crystal symmetry as a result of antiferromagnetic ordering ͑ϳ0.6°for MnO and ϳ0.07°for NiO away from cubic 16 ͒.…”

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confidence: 99%

Broken symmetry, strong correlation, and splitting between longitudinal and transverse optical phonons of MnO and NiO from first principles

et al. 2010

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We propose a first-principles scheme, using the distorted structure, to obtain the phonons of the undistorted parent structure for systems with both broken symmetry as well as the splitting between longitudinal optical and transverse optical ͑TO͒ phonon modes due to long-range dipole-dipole interactions. Broken symmetry may result from antiferromagnetic ordering or structural distortion. Applications to the calculations of the phonon dispersions of NiO and MnO, the two benchmark Mott-Hubbard systems with the TO mode splitting for MnO, show remarkable accuracy.With advances in calculating atomic force constants within the framework of density-functional perturbation theory 1 and density-functional theory, 2 first-principles calculations can now predict electronic and vibrational properties for many classes of materials, including simple metals, transition metals, intermetallics, semiconductors, hydrides, and earth materials with exceptional accuracy. 3 However, it has been difficult to predict the lattice dynamics for strongly correlated electronic systems, particularly Mott-Hubbard insulators. These include materials such as NiO and MnO, 4-8 the La 2 CuO 4 -based cuprate superconductors, 9 and the LaMnO 3 -based colossal magnetoresistance manganites. 10 Experimental measurements also yielded inconsistent results on the frequency values of the optical phonons for both MnO ͑Refs. 6 and 8͒ and NiO. 5,7 The specific difficulties 11-15 in predicting the lattice dynamics of Mott-Hubbard insulators are: ͑i͒ the highly correlated nature of electronic states in these materials and ͑ii͒ the slight lowering of crystal symmetry as a result of antiferromagnetic ordering ͑ϳ0.6°for MnO and ϳ0.07°for NiO away from cubic 16 ͒.In this work, we report a scheme to accurately compute phonon dispersions of Mott-Hubbard systems such as MnO and NiO. This involves a combination of a method for recovering the ideal cubic symmetry from the slightly distorted structure, the mixed-space approach 17 for treating the splitting between longitudinal optical ͑LO͒ and transverse optical ͑TO͒ phonon modes, and the density-functional theory ͑DFT͒ plus U method for accounting for the strong electron correlation. 18 In applying the direct approach to predict the phonon dispersions of polar materials, a lot of effort 19-23 has been made to treat the contribution of the nonanalytical term. The mixed-space approach makes it parameter-free to accurately determine the phonon frequencies using the direct approach for polar materials. 17 In this approach, the force constants are written aswhere ⌽ ␣␤ jk is the interaction force-constant between atom j in the primitive cell M and atom k in the primitive cell P, ␣␤ jk the contribution from short-range interactions, N the number of primitive unit cells in the supercell, and D ␣␤ jk ͑na ; q → 0͒ the contribution from long-range interactions, i.e., the so-called nonanalytical part of the dynamical matrix in the limit of zero wave vector q. According to Cochran and Cowley 24

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“…17,18 The OPENPHONON source code 19 was used for the calculations, and most of the parameters were taken from Ref. 17.…”

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confidence: 99%

Effects of anisotropic charge on transverse optical phonons in NiO: Inelastic x-ray scattering spectroscopy study

2010

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Phonon dispersion of detwinned NiO is measured using inelastic x-ray scattering. It is found that, near the zone center, the energy of the transverse-optical-phonon mode polarized parallel to the antiferromagnetic order is ϳ1 meV lower than that of the mode polarized perpendicular to the order, at room temperature. This is explained via anisotropic polarization of the Ni and O atoms, as confirmed using a Berry's phase approach with first-principles calculations. Our explanation avoids an apparent contradiction in previous discussions focusing on Heisenberg interaction.Transition-metal mono-oxides are fundamental materials for studying properties of magnetic and strongly correlated systems. Among them, NiO and MnO are antiferromagnetic ͑AFM͒ insulators with similar crystal structure and physical properties. The AFM order and lattice contraction occur along the ͓111͔ direction below the Néel temperature ͑T N = 523 K for NiO͒. The order consists of ferromagnetic ͑111͒ planes. Above T N , both have a rocksalt structure. NiO and MnO are relatively simple, because they have nondegenerate electronic ground states, and are free from Jahn-Teller effects, unlike FeO and CoO. 1 The magnetism of these materials is often discussed in terms of a superexchange mechanism. MnO has antiferromagnetic interactions both in the nearest-neighbor ͑J 1 ͒ and next-nearest-neighbor ͑J 2 ͒ exchanges, and these interactions reproduce the experimental results. 2,3 On the other hand, J 1 for NiO still remains uncertain, perhaps because it is much smaller than the antiferromagnetic superexchange J 2 interaction, which is responsible for the AFM order. For example, local spin-density approximation ͑LSDA͒ + U calculations give ferromagnetic J 1 ͑Ref. 3͒ while some calculations such as GW show antiferromagnetic J 1 . 4 Experimentally, a measurement of spin-wave dispersion indicates ferromagnetic J 1 ͑Ref. 5͒ while one of magnetic susceptibility suggests antiferromagnetic J 1 . 6 Another issue is that LSDA+ U calculation results are not easily reconciled with the exchange-interaction picture of NiO. According to Refs. 2 and 7, the lattice distortion is dominated by J 1 with no contribution from J 2 , and antiferromagnetic J 1 causes the contraction in ͓111͔, if ͉J 1 ͉ decreases with increasing the distance between the nearest-neighbor Ni atoms. Based on this discussion, the calculated ferromagnetic J 1 ͑Ref. 3͒ is not consistent with the calculated 8 ͑and observed͒ contraction in NiO, suggesting an additional ingredient is needed to understand the calculation results.The energy of transverse optical ͑TO͒ phonons can be used as a direct probe of microscopic coupling; 9 TO modes that would be degenerate in a cubic rocksalt structure, are split at the zone center under the AFM order, with the energy of the mode polarized along the order ͑E ʈ TO ͒ different than that of the mode polarized in the plane perpendicular to the order ͑E Ќ TO ͒. As discussed in Ref. 3 the sign of this difference ͑E ʈ TO − E Ќ TO ͒ can be linked to the sign of J 1 . The pict...

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Lattice dynamics of NiO

Cited by 80 publications

References 20 publications

Role of electronic correlations on the phonon modes of MnO and NiO

Role of electronic correlations on the phonon modes of MnO and NiO

Broken symmetry, strong correlation, and splitting between longitudinal and transverse optical phonons of MnO and NiO from first principles

Effects of anisotropic charge on transverse optical phonons in NiO: Inelastic x-ray scattering spectroscopy study

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