Chemical tuning of the optical band gap in spinel ferrites: CoFe2O4 vs NiFe2O4

Holinsworth, B. S.; Mazumdar, Dipanjan; Sims, Hunter; Sun, Qi; Yurtisigi, Mehmet; Sarker, Sanjoy K.; Gupta, Arunava; Butler, W. H.; Musfeldt, J. L.

doi:10.1063/1.4818315

Cited by 179 publications

(85 citation statements)

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“…4 depicts the optical absorption spectrum of an NFO film in an energy range from 0.8 eV to 5.6 eV. Experimental data by Holinsworth et al 28,29 and a calculated spectrum by Meinert et al 30 are shown for comparison. The absorption coefficient α(E) was obtained from the measured transmission and reflectance spectra by α = .…”

Section: Electronic Propertiesmentioning

confidence: 99%

Physical characteristics and cation distribution of NiFe2O4 thin films with high resistivity prepared by reactive co-sputtering

Klewe¹,

Meinert²,

Boehnke³

et al. 2014

Journal of Applied Physics

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We fabricated NiFe 2 O 4 thin films on MgAl 2 O 4 (001) substrates by reactive dc magnetron co-sputtering in a pure oxygen atmosphere at different substrate temperatures. The film properties were investigated by various techniques with a focus on their structure, surface topography, magnetic characteristics, and transport properties. Structural analysis revealed a good crystallization with epitaxial growth and low roughness and a similar quality as in films grown by pulsed laser deposition. Electrical conductivity measurements showed high room temperature resistivity (12 Ωm), but low activation energy, indicating an extrinsic transport mechanism. A band gap of about 1.55 eV was found by optical spectroscopy. Detailed x-ray spectroscopy studies confirmed the samples to be ferrimagnetic with fully compensated Fe moments. By comparison with multiplet calculations of the spectra we found that the cation valencies are to a large extent Ni 2+ and Fe 3+ .

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Section: Electronic Propertiesmentioning

confidence: 99%

Physical characteristics and cation distribution of NiFe2O4 thin films with high resistivity prepared by reactive co-sputtering

Klewe¹,

Meinert²,

Boehnke³

et al. 2014

Journal of Applied Physics

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“…This is comparable with the conventional ferroelectrics and therefore implies the presence of spontaneous polarization in the bulk NFO. However, the ferroelectricity of bulk NFO has neither been calculated nor measured yet, though the intensive studies of electronic [32][33][34], magnetic [35], and epitaxial strain and magnetoelastic properties [36][37][38] Fe 3+ and Ni 2+ over B-sites in the F d3m unit cell with the periodic boundary condition rather than in infinite bulk crystal, it might be possible to generate different space groups whose symmetries are lowered from F d3m. It is only recent year that, through the Raman spectra measurements, both NFO single crystals [39] and thin films [40] exhibit short range B-site ordering with tetragonal P 4 1 22 (No.…”

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confidence: 99%

“…This is comparable with the conventional ferroelectrics and therefore implies the presence of spontaneous polarization in the bulk NFO. However, the ferroelectricity of bulk NFO has neither been calculated nor measured yet, though the intensive studies of electronic [32][33][34], magnetic [35], and epitaxial strain and magnetoelastic properties [36][37][38] have been conducted.Which is the most stable structure?-It is well accepted that NFO crystallizes in the completely inverse spinel structure with a face-centered cubic space group F d3m (No. 227), where half of the Fe 3+ cations occupy the tetrahedral A-sites (8a), the rest of Fe 3+ and Ni 2+ cations are equally distributed over the octahedral B-sites (16d), and the sites of oxygen anions are distinguished into O 1 and O 2 .…”

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First-principles study of ferroelectricity induced by p–d hybridization in ferrimagnetic NiFe 2 O 4

Jong¹,

Yu²,

Park³

et al. 2016

Physics Letters A

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We investigate the ferrimagnetism and ferroelectricity of bulk NiFe2O4 with tetragonal P 4122 symmetry by means of density functional calculations using generalized gradient approximation + Hubbard U approach. Special attention is paid to finding the most energetically favorable configuration on magnetic ordering and further calculating the reliable spontaneous electric polarization. With the fully optimized crystalline structure of the most stable configuration, the spontaneous polarization is obtained to be 23 µC/cm 2 along the z direction, which originates from the hybridization between the 3d states of the Fe 3+ cation and the 2p states of oxygen induced by Jahn-Teller effect.PACS numbers: 41.20. Gz, 75.85.+t,Magnetic ferroelectrics that possess ferroelectricity together with some form of magnetic order like ferromagnetic, antiferromagnetic, or ferrimagnetic property in the same crystalline phase have attracted much interest due to their fundamental physics and a great promise for applications in future information technology [2][3][4][5][6][7][8]. In particular, improper multiferroics in which a ferroelectric polarization is induced by electronic correlation effects such as non-centrosymmetric spin, charge, and orbital ordering, is currently under intensive study [9][10][11][12]. This is related to the suggestion that a magneto-electric (ME) coupling in improper multiferroics is expected to be stronger than in proper case, because both dipolar and magnetic orderings share the same physical origin and occur at the same temperature [9].In the early days of searching improper multiferroics, spin ordering was accepted to be a main driving force for the manifestation of ferroelectric polarization; examples include rare earth manganites RMnO 3 [13][14][15][16] [10] are typical compounds belonged to this materials class. These materials have weak ferromagnetism and thus a significant ME coupling is expected. Despite the great progress in the field of improper multiferroics, the effort to find new mechanism and design new materials is being continued.In this letter, we present that spinel-type nickel ferrite NiFe 2 O 4 (NFO) is a promising candidate for improper multiferroics with finite magnetization and considerably large polarization, based on the first-principles density functional theory (DFT) calculations. In fact, spinels exhibit several unusual features including magnetoelectricity and multiferroicity [9]. From the experiment, it was established that the bulk NFO shows soft ferrimagnetic ordering below relatively high transition temperature of 850 K with a magnetization of 2 µ B per formula unit (f.u.) [30]. In the recent experiment [31], moreover, high dielectric permitivity was observed in NFO nanoparticles to be ranged from 60 to 600 at different frequencies and temperatures. This is comparable with the conventional ferroelectrics and therefore implies the presence of spontaneous polarization in the bulk NFO. However, the ferroelectricity of bulk NFO has neither been calculated nor measured yet, though ...

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“…Our calculated band-gap energies and magnetic moments are close to those calculated by other groups [25,[51][52][53], and to the experimental indirect band gap of 1.2 eV measured by optical measurements [52]. The calculated band gap of MgAl 2 O 4 is of 5.13 eV, lower than the 7.8 eV measured experimentally and reported in Ref.…”

Section: Discussionmentioning

confidence: 35%

Fully spin-polarized two-dimensional electron gas at the <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi mathvariant="normal">CoFe</mi></mrow><mn>2</mn></msub><msub><mrow><mi mathvariant="normal">O</mi></mrow><mn>4</mn></msub><mo>/</mo><msub><mrow><mi mathvariant="normal">MgAl</mi></mrow><mn>2</mn>

Arras

Calmels

2014

Phys. Rev. B

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We performed first-principles calculations to show that a fully spin-polarized two-dimensional electron gas can be created at the interface between the polar and insulating spinel oxides CoFe 2 O 4 and MgAl 2 O 4 . We give a clear description of the physical parameters (in particular the atomic termination of the interfaces), which favor the formation of this electron gas that is due either to an electric field induced in stoichiometric oxide layers because of their polar character or to a charge reorganization that preserves the global electric neutrality in nonstoichiometric layers. We show that the electric field-induced spin-polarized two-dimensional electron gas can only exist if the thickness of the CoFe 2 O 4 layer is large enough and that it may be destroyed by intermixing at the interfaces.

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Chemical tuning of the optical band gap in spinel ferrites: CoFe₂O₄ vs NiFe₂O₄

Cited by 179 publications

References 38 publications

Physical characteristics and cation distribution of NiFe2O4 thin films with high resistivity prepared by reactive co-sputtering

Physical characteristics and cation distribution of NiFe2O4 thin films with high resistivity prepared by reactive co-sputtering

First-principles study of ferroelectricity induced by p–d hybridization in ferrimagnetic NiFe 2 O 4

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