Electronic and magnetic structure of transition-metal-doped<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math>-hematite

Velev, Julian P.; Bandyopadhyay, Amrit; Butler, W. H.; Sarker, Sanjoy K.

doi:10.1103/physrevb.71.205208

Cited by 93 publications

(58 citation statements)

References 15 publications

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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.…”

supporting

confidence: 82%

“…We find that incorporation in the same spin-sublattice T 5,10 (which maximizes the magnetic moment) is favored by 0.22 eV compared to the AFM T 5,7 . Taking into account local lattice relaxations enhances the energy gain compared to previous calculations by Velev et al (0.08 eV) [22]. Still, some degree of Ti disorder is likely in quickly cooled samples, reducing the expected magnetization as observed by Chambers et al [3] (0.5±0.15µ B /Ti for x Ti = 0.15).…”

Section: Or T 58mentioning

confidence: 55%

“…However, electronic correlations, not included in the local (spin-) density approximation (LSDA) or GGA of DFT, play an important role in transition metal oxides. Such effects were considered recently within LSDA+U [22] or using hybrid functionals [23] for …”

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confidence: 99%

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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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supporting

confidence: 82%

Section: Or T 58mentioning

confidence: 55%

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Interface magnetism inFe2O3/FeTiO3heterostructures

Pentcheva¹,

Nabi²

2008

Phys. Rev. B

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“…In the Co-doped α-Fe 2 O 3 NAs, the enhanced coercivity could be due to the well-known spin-orbit coupling strength of Co 2+ cations and the redistribution of cations. 24 The Co-doped α-Fe 2 O 3 NAs, synthesized in the magnetic field shows further improvement in H C to 5.5 kOe. As the synthesis was performed under the influence of a strong magnetic field, the nanocrystals are gradually arranged to a three-dimensional (3D) cubic assembly through oriented attachment.…”

Section: Experimental Methodsmentioning

confidence: 99%

Enhanced coercivity in Co-doped α-Fe2O3 cubic nanocrystal assemblies prepared via a magnetic field-assisted hydrothermal synthesis

et al. 2017

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Ferromagnetic Co-doped α-Fe2O3 cubic shaped nanocrystal assemblies (NAs) with a high coercivity of 5.5 kOe have been synthesized via a magnetic field (2 kOe) assisted hydrothermal process. The X-ray diffraction pattern and Raman spectra of α-Fe2O3 and Co-doped α-Fe2O3 NAs confirms the formation of single-phase α-Fe2O3 with a rhombohedral crystal structure. Electron microscopy analysis depict that the Co-doped α-Fe2O3 NAs synthesized under the influence of the magnetic field are consist of aggregated nanocrystals (∼30 nm) and of average assembly size 2 μm. In contrast to the NAs synthesized with no magnetic field, the average NAs size and coercivity of the Co-doped α-Fe2O3 NAs prepared with magnetic field is increased by 1 μm and 1.4 kOe, respectively. The enhanced coercivity could be related to the well-known spin–orbit coupling strength of Co2+ cations and the redistribution of the cations. The size increment indicates that the small ferromagnetic nanocrystals assemble into cubic NAs with increased size in the magnetic field that also lead to the enhanced coercivity.

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“…Basic mechanism of the unusual magnetic, electric and electro-magnetic properties in metal doped α-Fe 2 O 3 (hematite) lies on the modifications of rhombohedral (111) planes of crystal structure. 8,9 Moreover, electromagnetic properties of metal doped α-Fe 2 O 3 samples are largely affected by the modified band structure. 10,11 This is important for developing magnetoelectronic materials for spintronics devices.…”

Section: Introductionmentioning

confidence: 99%

Magnetic, dielectric and photo-absorption study of a ferromagnetic semiconductor α-Fe1.4Ga0.6O3

Naresh

Bhowmik

2011

AIP Advances

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We report the synthesis of α-Fe1.4Ga0.6O3 compound and present its structural phase stability and interesting magnetic, dielectric and photo-absorption properties. In our work Ga doped α-Fe2O3 samples are well stabilized in α phase (rhombohedral crystal structure with space group R3C). Properties of the present composition of Ga doped α-Fe2O3 system are remarkably advanced in comparison with recently most studied FeGaO3 composition. At room temperature the samples are typical soft ferromagnet, as well as direct band gap semiconductor. Dielectric study showed low dielectric loss in the samples with large enhancement of ac conductivity at higher frequencies. Optical absorption in the visible range has been enhanced by 4 to 5%. This composition has exhibited large scope of tailoring room temperature ferromagnetic moment and optical band gap by varying grain size and non-ambient (vacuum) heat treatment of the as prepared samples by mechanical alloying.

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Electronic and magnetic structure of transition-metal-dopedα-hematite

Cited by 93 publications

References 15 publications

Interface magnetism inFe2O3/FeTiO3heterostructures

Interface magnetism inFe2O3/FeTiO3heterostructures

Enhanced coercivity in Co-doped α-Fe2O3 cubic nanocrystal assemblies prepared via a magnetic field-assisted hydrothermal synthesis

Magnetic, dielectric and photo-absorption study of a ferromagnetic semiconductor α-Fe1.4Ga0.6O3

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