First-principles calculation of the structure and magnetic phases of hematite

Rollmann, Georg; Rohrbach, Alexander; Entel, P.; Häfner, J.

doi:10.1103/physrevb.69.165107

Cited by 435 publications

(422 citation statements)

References 52 publications

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“…45 In the present study we use the DFT+U approach, as formulated by Dudarev 46 and implemented in the VASP code, 47,48 using the generalized gradient approximation (GGA) and the Perdew-Wang 91 (PW91) functional 49 (plane wave basis set with the kinetic energy cut off of 400 eV, and projected augmented wave (PAW) method 50,51 ). Similarly to the existing studies on iron oxides (hematite in the GGA+U approach 52 ), we obtain a satisfactory description of distorted B1 bulk properties for U = 4 eV and J = 1 eV. In particular, we find a type-II AFM insulating ground state with a band gap of 1.4 eV in line with previous calculations.…”

Section: Computational Methods and Modelssupporting

confidence: 71%

Interplay between structural, magnetic, and electronic properties in aFeO∕Pt(111)ultrathin film

et al. 2007

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We have investigated the magnetic and electronic properties of a FeO film grown on Pt(111).Coupling first principle GGA+U calculations with STM measurements we have identified the principal mechanisms for the structural and electronic non-homogeneous characteristics observed in the Moiré unit cell formed between oxide film and metal support. We show that both free and supported FeO(111) monolayers present an anti-parallel alignment of the magnetic moments and that the modulation of structural and electronic film properties is driven by the local strength of the interaction between the film and the substrate. Namely, due to the lattice mismatch between Pt (111) and the FeO film, the interface properties are different in different regions of the supercell. In particular, for the Fe-top site, where this interaction is weak, the resulting small layer rumpling and large interface separation give origin to a peculiar behavior of the work function, coherent with the most recent experimental findings. In what concerns fine structural and electronic characteristics, in particular the modulation of the work function and the site assignment in the STM images, our results show that a good agreement with the experimental interpretations can be obtained only within more robust, non-pseudomorphic computational models.

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Section: Computational Methods and Modelssupporting

confidence: 71%

Interplay between structural, magnetic, and electronic properties in aFeO∕Pt(111)ultrathin film

et al. 2007

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“…In agreement with previous calculations [22,28], GGA+U considerably improves the band gap of hematite from 0.43 eV (GGA) to 2.2 eV for U=6 eV and J=1 eV in close agreement with measured values of 2.14-2.36 eV [29,30]. Also the type of band gap changes from a Mott-Hubbard between Fe3d-Fe3d states to charge transfer after the scheme of Zaanen et al [31] between occupied O2p and empty Fe3d-states.…”

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confidence: 82%

Interface magnetism inFe2O3/FeTiO3heterostructures

Pentcheva¹,

Nabi²

2008

Phys. Rev. B

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To resolve the microscopic origin of magnetism in the Fe2O3/FeTiO3-system, we have performed density functional theory calculations taking into account on-site Coulomb repulsion. By varying systematically the concentration, distribution and charge state of Ti in a hematite host, we compile a phase diagram of the stability with respect to the end members and find a clear preference to form layered arrangements as opposed to solid solutions. The charge mismatch at the interface is accommodated through Ti 4+ and a disproportionation in the Fe contact layer into Fe 2+ , Fe 3+ , leading to uncompensated moments in the contact layer and giving first theoretical evidence for the lamellar magnetism hypothesis. This interface magnetism is associated with impurity levels in the band gap showing halfmetallic behavior and making Fe2O3/FeTiO3 heterostructures prospective materials for spintronics applications.A challenge of today's materials science is to design ferromagnetic semiconductors operating at room-temperature (RT) for spintronics devices. Most of the efforts concentrate on homogeneous doping of semiconductors with magnetic impurities [1,2,3,4], but the interfaces in complex oxides prove to be another source of novel behavior [5,6,7]. The unique magnetic properties of the hematiteilmenite system [8, 9, 10] (a canted antiferromagnet and a RT paramagnet, respectively) currently receive revived interest as a possible cause of magnetic anomalies in the Earth's deep crust and on other planets [11] as well as for future device applications [3,12,13].Both hematite (a = 5.035Å, c = 13.751Å [14]) and ilmenite (a = 5.177Å, c = 14.265Å [15]) crystallize in a corundum(-derived) structure shown in Fig. 1 where the oxygen ions form a distorted hexagonal close packed lattice and the cations occupy 2/3 of the octahedral sites. In α-Fe 2 O 3 (space group R3c) there is a natural modulation of electronic density along the [0001]-direction where negatively charged 3O 2− layers alternate with positively charged 2Fe 3+ layers. At RT the magnetic moments of subsequent iron layers couple antiferromagnetically (AFM) in-plane with a small spin-canting, attributed to spin-orbit coupling [16,17,18]. In ilmenite, FeTiO 3 , Fe-and Ti-layers alternate, reducing the symmetry to R3 and the corresponding sequence is 3O 2− /2Fe 2+ /3O 2− /2Ti 4+ with AFM coupling between the Fe layers and T N =56-59 K [19].At the interfaces (IFs) in hematite-ilmenite exsolutions, charge neutrality is disrupted. One way to balance the excess charge at the interface is by a disproportionation in the Fe layer, now becom- * Electronic address: pentcheva@lrz.uni-muenchen.de ing mixed Fe 2+ and Fe 3+ . This lamellar magnetism hypothesis (LMH) was proposed by Robinson et al. [20] based on bond valence models and kinetic Monte Carlo simulations (kMC) with empirical chemical and magnetic interaction parameters. The increased technological interest in this system calls for an atomistic material specific understanding that can only be obtained from first principles calculatio...

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“…Recently, however, the use of U eff has been shown to improve the structural properties of transition-metal sulfides 35 and hematite. 36 Rock-salt ͑G-type͒ antiferromagnetic ͑AFM͒ order is assumed for all calculations, as well as a homogeneous and collinear spin arrangement. This assumption is well justified, However, experiments also report a long-wavelength spiral spin structure 37 and possibly a small out-of-plane canting due to weak ferromagnetism.…”

Section: Methodsmentioning

confidence: 99%

First-principles study of spontaneous polarization in multiferroicBiFeO3

et al. 2005

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The ground-state structural and electronic properties of ferroelectric BiFeO 3 are calculated using density functional theory within the local spin-density approximation ͑LSDA͒ and the LSDA+ U method. The crystal structure is computed to be rhombohedral with space group R3c, and the electronic structure is found to be insulating and antiferromagnetic, both in excellent agreement with available experiments. A large ferroelectric polarization of 90-100 C/cm 2 is predicted, consistent with the large atomic displacements in the ferroelectric phase and with recent experimental reports, but differing by an order of magnitude from early experiments. One possible explanation is that the latter may have suffered from large leakage currents. However, both past and contemporary measurements are shown to be consistent with the modern theory of polarization, suggesting that the range of reported polarizations may instead correspond to distinct switching paths in structural space. Modern measurements on well-characterized bulk samples are required to confirm this interpretation.

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First-principles calculation of the structure and magnetic phases of hematite

Cited by 435 publications

References 52 publications

Interplay between structural, magnetic, and electronic properties in aFeO∕Pt(111)ultrathin film

Interplay between structural, magnetic, and electronic properties in aFeO∕Pt(111)ultrathin film

Interface magnetism inFe2O3/FeTiO3heterostructures

First-principles study of spontaneous polarization in multiferroicBiFeO3

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