Europium chalcogenide magnetic semiconductor nanostructures

Boncher, William L.; Dalafu, Haydee; Rosa, Nicholas; Stoll, Sarah L.

doi:10.1016/j.ccr.2014.12.008

Cited by 40 publications

(35 citation statements)

References 110 publications

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“…Developing quantitative descriptions for chemical structure and bonding in lanthanide compounds that are grounded by both theory and experiment is a longstanding challenge in physical and inorganic chemistry. [1][2][3][4][5][6][7][8][9][10][11][12] This is especially true for the lanthanide dioxides, LnO 2 (Ln = Ce, Pr, Tb), which are the only stable dioxides formed by lanthanides, and among the only stable compounds of Pr and Tb in the +4 formal oxidation states. [13][14] A better theoretical understanding of Ln-O bonding in these materials is necessary to understand the rates and mechanisms of conversion between LnO 2 and the substoichiometric oxides, LnO 2-x (where 0 > x > 0.5), via diffusion of lanthanide and oxygen ions, which features prominently in many energy-related technologies.…”

Section: Introductionmentioning

confidence: 99%

Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO₂, PrO₂, and TbO₂

et al. 2017

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Understanding the nature of covalent (band-like) vs ionic (atomic-like) electrons in metal oxides continues to be at the forefront of research in the physical sciences. In particular, the development of a coherent and quantitative model of bonding and electronic structure for the lanthanide dioxides, LnO (Ln = Ce, Pr, and Tb), has remained a considerable challenge for both experiment and theory. Herein, relative changes in mixing between the O 2p orbitals and the Ln 4f and 5d orbitals in LnO are evaluated quantitatively using O K-edge X-ray absorption spectroscopy (XAS) obtained with a scanning transmission X-ray microscope and density functional theory (DFT) calculations. For each LnO, the results reveal significant amounts of Ln 5d and O 2p mixing in the orbitals of t (σ-bonding) and e (π-bonding) symmetry. The remarkable agreement between experiment and theory also shows that significant mixing with the O 2p orbitals occurs in a band derived from the 4f orbitals of a symmetry (σ-bonding) for each compound. However, a large increase in orbital mixing is observed for PrO that is ascribed to a unique interaction derived from the 4f orbitals of t symmetry (σ- and π-bonding). O K-edge XAS and DFT results are compared with complementary L-edge and M-edge XAS measurements and configuration interaction calculations, which shows that each spectroscopic approach provides evidence for ground state O 2p and Ln 4f orbital mixing despite inducing very different core-hole potentials in the final state.

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Section: Introductionmentioning

confidence: 99%

Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO₂, PrO₂, and TbO₂

et al. 2017

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“…1(b)]. The Heisenberg interaction, superexchange interaction [25,28], d − f coupling [29] and coupling with the TI's spin texture may finally contribute to an overall augmentation of the proximity effect.…”

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confidence: 99%

Proximity-Driven Enhanced Magnetic Order at Ferromagnetic-Insulator–Magnetic-Topological-Insulator Interface

Chang

Kirby

et al. 2015

Phys. Rev. Lett.

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Magnetic exchange driven proximity effect at a magnetic-insulator-topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. Here we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic-TI EuS=Sb 2−x V x Te 3 hybrid heterostructure, where V doping is used to drive the TI (Sb 2 Te 3 ) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magnetic ordering. The time-reversal symmetry (TRS) breaking and surface band gap opening of a topological insulator (TI) are essential ingredients necessary for towards the observation of novel quantum phases and realization for TI-based devices [1,2]. In general, there are two approaches to break the TRS: transitional-metal (TM) ion doping [3][4][5] and magnetic proximity effect where a magnetic insulator (MI) adlayer induces exchange coupling [3,[6][7][8]. Doping TM impurities into a TI will introduce a perpendicular ferromagnetic (FM) anisotropy and provide a straightforward means to open up the band gap of a TI's surface state, with profound influence to its electronic structure [4,[9][10][11][12][13][14]. In particular, quantum anomalous Hall effect (QAHE), where quantum Hall plateau and dissipationless chiral edge channels emerge at zero external magnetic field, has recently been realized in Cr-doped and V-doped TIs [9,10,[15][16][17][18][19][20]. Ideally, compared to the doping method, proximity effect has a number of advantages, including spatially uniform magnetization, better controllability of surface state, freedom from dopant-induced scattering, as well as preserving TI intrinsic crystalline structure, etc. [21,22]. However, due to the inplane anisotropy and low Curie temperature, such MIs are usually too weak to induce strong proximity magnetism in a TI. In fact, compared to a magnetically doped TI which can induce as large as a 50 meV surface band gap [4], the EuS-TI system has only a 7 meV gap opening due to the strongly localized Eu f orbitals [23]. Therefore, the enhancement of proximity magnetism is highly desirable to make it a valuable approach as doping hence takes full advantage.In this Letter, we report significant enhancement of the proximity effect in MI EuS/magnetic-TI Sb 2−x V x Te 3 hybrid heterostructure. Using polarized neutron reflectometry (PNR), we inferred an increase of proximity magnetization per unit cell (u.c.) in TI, from 1.2μ B =u:c. to 2.7μ B =u:c. at x ¼ 0.1 doping level. High-resolution transmission electron microscopy (HRTEM) identifies the TI-EuS interfacial sharpness and excludes the false positive magnetism signal from interdiffused Eu ions into a TI. Furthermore, the proximity effect enhancement is accompanied by a decrease of the interfacial magnetization of EuS, resulting in an exotic antiferro...

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“…A general review paper has been published in 1968 [13], followed by Mössbauer spectroscopy on iron [14], glass [15,16,17], Fe/S proteins [18], and europium chalcogenides [19] among others. No review paper is known for the investigation of europium luminescence using Mössbauer spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Luminescent Materials with 151Eu Mössbauer Spectroscopy

Steudel

Johnson

et al. 2018

Materials

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The application of Mössbauer spectroscopy to luminescent materials is described. Many solids doped with europium are luminescent, i.e., when irradiated with light they emit light of a longer wavelength. These materials therefore have practical applications in tuning the light output of devices like light emitting diodes. The optical properties are very different for the two possible valence states Eu2+ and Eu3+, the former producing ultraviolet/visible light that shifts from violet to red depending on the host and the latter red light, so it is important to have a knowledge of their behavior in a sample environment. Photoluminescence spectra cannot give a quantitative analysis of Eu2+ and Eu3+ ions. Mössbauer spectroscopy, however, is more powerful and gives a separate spectrum for each oxidation state enabling the relative amount present to be estimated. The oxidation state can be identified from its isomer shift which is between −12 and −15 mm/s for Eu2+ compared to around 0 mm/s for Eu3+. Furthermore, within each oxidation state, there are changes depending on the ligands attached to the europium: the shift is more positive for increased covalency of the bonding ligand X, or Eu concentration, and decreases for increasing Eu–X bond length.

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Europium chalcogenide magnetic semiconductor nanostructures

Cited by 40 publications

References 110 publications

Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO₂, PrO₂, and TbO₂

Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO₂, PrO₂, and TbO₂

Proximity-Driven Enhanced Magnetic Order at Ferromagnetic-Insulator–Magnetic-Topological-Insulator Interface

Characterization of Luminescent Materials with 151Eu Mössbauer Spectroscopy

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Europium chalcogenide magnetic semiconductor nanostructures

Cited by 40 publications

References 110 publications

Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO2, PrO2, and TbO2

Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO2, PrO2, and TbO2

Proximity-Driven Enhanced Magnetic Order at Ferromagnetic-Insulator–Magnetic-Topological-Insulator Interface

Characterization of Luminescent Materials with 151Eu Mössbauer Spectroscopy

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Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO₂, PrO₂, and TbO₂

Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO₂, PrO₂, and TbO₂