On-site approximation for spin–orbit coupling in linear combination of atomic orbitals density functional methods

Fernández-Seivane, Lucas; Oliveira, Marco Aurélio Souza; Sanvito, Stefano; Ferrer, Jaime

doi:10.1088/0953-8984/18/34/012

Cited by 120 publications

(121 citation statements)

References 44 publications

(57 reference statements)

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“…For the Mn basis set, 3p orbitals as a semicore are required in order for the molecular orbital levels of an isolated Mn 12 to be comparable to those obtained from allelectron calculations. 42 With these pseudopotentials and basis sets, self-consistent DFT calculations including spin-orbit coupling 37 are performed for an isolated Mn 12 . Using a modified version 37 of SIESTA, we obtain the total magnetic moment of 20 B and the magnetic anisotropy barrier of 66.4 K. 14 This is in good agreement with experiment 33 and with the barrier 43,44 computed using the DFT code VASP.…”

Section: Computational Methods and Modelmentioning

confidence: 99%

“…42 With these pseudopotentials and basis sets, self-consistent DFT calculations including spin-orbit coupling 37 are performed for an isolated Mn 12 . Using a modified version 37 of SIESTA, we obtain the total magnetic moment of 20 B and the magnetic anisotropy barrier of 66.4 K. 14 This is in good agreement with experiment 33 and with the barrier 43,44 computed using the DFT code VASP. 45 To reduce the computational cost, a small Au basis set of a single s orbital is used for transport calculations while a large Au basis set of both d and s orbitals is used for geometry relaxation.…”

Section: Computational Methods and Modelmentioning

confidence: 99%

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Effects of bonding type and interface geometry on coherent transport through the single-molecule magnetMn12

et al. 2010

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We examine theoretically coherent electron transport through the single-molecule magnet Mn 12 , bridged between Au͑111͒ electrodes, using the nonequilibrium Green's function method and the density-functional theory. We analyze the effects of bonding type, molecular orientation, and geometry relaxation on the electronic properties and charge and spin transport across the single-molecule junction. We consider nine interface geometries leading to five bonding mechanisms and two molecular orientations: ͑i͒ Au-C bonding, ͑ii͒ Au-Au bonding, ͑iii͒ Au-S bonding, ͑iv͒ Au-H bonding, and ͑v͒ physisorption via van der Waals forces. The two molecular orientations of Mn 12 correspond to the magnetic easy axis of the molecule aligned perpendicular ͓hereafter denoted as orientation ͑1͔͒ or parallel ͓orientation ͑2͔͒ to the direction of electron transport. We find that the electron transport is carried by the lowest unoccupied molecular orbital ͑LUMO͒ level in all the cases that we have simulated. Relaxation of the junction geometries mainly shifts the relevant occupied molecular levels toward the Fermi energy as well as slightly reduces the broadening of the LUMO level. As a result, the current slightly decreases at low bias voltage. Our calculations also show that placing the molecule in the orientation ͑1͒ broadens the LUMO level much more than in the orientation ͑2͒ due to the internal structure of the Mn 12 . Consequently, junctions with the former orientation yield a higher current than those with the latter. Among all of the bonding types considered, the Au-C bonding gives rise to the highest current ͑about one order of magnitude higher than the Au-S bonding͒, for a given distance between the electrodes. The current through the junction with other bonding types decreases in the order of Au-Au, Au-S, and Au-H. Importantly, the spin-filtering effect in all the nine geometries stays robust and their ratios of the majority-spin to the minorityspin transmission coefficients are in the range of 10 3 -10 8 . The general trend in transport among the different bonding types and molecular orientations obtained from this study may be applicable to other single-molecule magnets.

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Section: Computational Methods and Modelmentioning

confidence: 99%

Section: Computational Methods and Modelmentioning

confidence: 99%

Effects of bonding type and interface geometry on coherent transport through the single-molecule magnetMn12

et al. 2010

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“…This post-self-consistent approach 14,31 is justified in the case of Ni, for which the SOC is much smaller than the exchange splittings and the bandwidths. We take = 70 meV for the Ni 3d orbitals.…”

Section: Model and Methodologymentioning

confidence: 99%

Anisotropic magnetoresistance in nanocontacts

2008

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We present ab initio calculations of the evolution of anisotropic magnetoresistance ͑AMR͒ in Ni nanocontacts from the ballistic to the tunnel regime. We find an extraordinary enhancement of AMR, compared to bulk, in two scenarios. In systems without localized states, such as chemically pure break junctions, large AMR only occurs if the orbital polarization of the current is large, regardless of the anisotropy of the density of states. In systems that display localized states close to the Fermi energy, such as a single electron transistor with ferromagnetic electrodes, large AMR is related to the variation of the Fermi energy as a function of the magnetization direction.

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“…1 we show the total energy as a function of the angle, ␣, between the magnetization and the WZ c axis for both CoO and ZnO:Co. These have been calculated from DFT including spin-orbit interaction 22 and using the local density approximation ͑LDA͒ of the exchange and correlation functional. One can immediately note that indeed DFT predicts the hard-axis easy-plane anisotropy found in EPR.…”

Section: Foundation Of the Model And Computational Detailsmentioning

confidence: 99%

Magnetism of wurtzite CoO nanoclusters

2010

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The possibility that the apparent room-temperature ferromagnetism, often measured in Co-doped ZnO, is due to uncompensated spins at the surface of wurtzite CoO nanoclusters is investigated by means of a combination of density-functional theory and Monte Carlo simulations. We find that the critical temperature extracted from the specific heat systematically drops as the cluster size is reduced, regardless of the particular cluster shape. Furthermore the presence of defects, in the form of missing magnetic sites, further reduces T C . This suggests that even a spinodal decomposed phase is unlikely to sustain room-temperature ferromagnetism in ZnO:Co. DOI: 10.1103/PhysRevB.81.054441 PACS number͑s͒: 75.50.Pp, 75.50.Tt, 75.75.Ϫc In recent years the search for ferromagnetism in insulating oxides doped with small quantities of transition metals has become a topic generating much debate in the literature. Taking ZnO:Co as the prototypical example for this class of materials, many experimental groups have reported roomtemperature ferromagnetism 1-3 whereas several other have failed to find any such evidence. 4,5 Notably, growth conditions, sample morphology, and spatial Co distribution play a crucial role in determining the magnetic properties. In particular, there is now an emerging view that samples with high structural quality and uniform Co distribution do not result in long-range ferromagnetism at high temperature and that the magnetism may be related to structural 6 or point defects. 7 Given the unsettled experimental landscape it should not be a surprise that a number of interesting and competing theoretical models have been proposed. In general explanations involving standard mechanisms for the magnetic interaction appear problematic. Schemes leading to short-range magnetic coupling such as superexchange need a Co concentration, ͓Co͔, exceeding the percolation threshold. This is around 20% for an interaction extending to the nearestneighbor sites of an fcc lattice and it is about a factor of five larger than the typical experimental concentrations. Similarly carrier-mediated mechanisms are not sustained by experimental evidence, which show both paramagnetism in presence of abundant-free carriers 6 and ferromagnetism deep in the insulating region of the phase diagram.2 More generally carrier concentration and mobility have an apparent little correlation to the magnetic properties.8 Furthermore carriermediated mechanisms are difficult to validate on a solid theoretical ground by using first-principles calculations since the empty Co d levels are usually erroneously predicted too shallow at the edge of the ZnO conduction band. 9Thus one has to look for more complex mechanisms for the magnetic interaction. Among these, the donor impurityband-exchange model ͑DIBE͒ ͑Ref. 10͒ has enjoyed considerable popularity in the experimental community. According to the DIBE the magnetic interaction among Co 2+ ions is mediated by donors, whose charge density is localized over large hydrogenic orbitals so that the relevant per...

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On-site approximation for spin–orbit coupling in linear combination of atomic orbitals density functional methods

Cited by 120 publications

References 44 publications

Effects of bonding type and interface geometry on coherent transport through the single-molecule magnetMn12

Effects of bonding type and interface geometry on coherent transport through the single-molecule magnetMn12

Anisotropic magnetoresistance in nanocontacts

Magnetism of wurtzite CoO nanoclusters

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