Direct observation of double exchange in ferromagnetic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>La</mml:mi><mml:mrow><mml:mn>0.7</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>Sr</mml:mi><mml:mrow><mml:mn>0.3</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>CoO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>by broadband ellipsometry

Friš, Pavel; Munzar, Dominik; Caha, Ondřej; Dubroka, Adam

doi:10.1103/physrevb.97.045137

Cited by 15 publications

(10 citation statements)

References 30 publications

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“…All samples show similar absorption behavior regardless of stoichiometry differences, implying similarities in optical band gaps and electronic structure. Absorption features are located at similar photon energies, with no additional peaks appearing due to either free carriers (Drude response [57]) or optical transitions from different cation site occupancy. Two clear absorption peaks (inset to Figure 5(b)) are centered around 0.8 eV and 1.9 eV, respectively.…”

Section: Resultsmentioning

confidence: 98%

Electronic and structural properties of single-crystal Jahn–Teller active Co_1+xMn_2−xO₄ thin films

Blanchet¹,

Heath²,

Kaspar³

et al. 2021

J. Phys.: Condens. Matter

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Recent investigations on spinel CoMn2O4 have shown its potential for applications in water splitting and fuel cell technologies as it exhibits strong catalytic behavior through oxygen reduction reactivity. To further understand this material, we report for the first time the synthesis of single-crystalline Co1+x Mn2−x O4 thin films using molecular beam epitaxy. By varying sample composition, we establish links between cation stoichiometry and material properties using in-situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry. Our results indicate that excess Co ions occupy tetrahedral interstitial sites at lower excess Co stoichiometries, and become substitutional for octahedrally-coordinated Mn at higher Co levels. We compare these results with density functional theory models of stoichiometric CoMn2O4 to understand how the Jahn–Teller distortion and hybridization in Mn–O bonds impact the ability to hole dope the material with excess Co. The findings provide important insights into CoMn2O4 and related spinel oxides that are promising candidates for inexpensive oxygen reduction reaction catalysts.

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Section: Resultsmentioning

confidence: 98%

Electronic and structural properties of single-crystal Jahn–Teller active Co_1+xMn_2−xO₄ thin films

Blanchet¹,

Heath²,

Kaspar³

et al. 2021

J. Phys.: Condens. Matter

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“…The nature of ferromagnetic state in the LSCO film is rather controversial due to the comparable energy competition between the crystal field splitting and the exchange interaction. 30 The most approved scenario for the ferromagnetic ordering in LSCO has been attributed to the double exchange between Co 3+ and Co 4+ high-spin state mediated via narrow t 2g orbitals. 31 For the treated LSCO a film, it exhibits a comparable ferromagnetic transition temperature as that of pristine LSCO film but a larger saturated magnetization of ∼0.78 μ B /Co.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Ferromagnetic Insulating Ground-State Resolved in Mixed Protons and Oxygen Vacancies-Doped La_0.67Sr_0.33CoO₃ Thin Films via Ionic Liquid Gating

Wu,

Shi,

et al. 2024

ACS Appl. Mater. Interfaces

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The realization of ferromagnetic insulating ground state is a critical prerequisite for spintronic applications. By applying electric field-controlled ionic liquid gating (ILG) to stoichiometry La0.67Sr0.33CoO3 thin films, the doping of protons (H+) has been achieved for the first time. Furthermore, a hitherto-unreported ferromagnetic insulating phase with a remarkably high T c up to 180 K has been observed which can be attributed to the doping of H+ and the formation of oxygen vacancies (VO). The chemical formula of the dual-ion migrated film has been identified as La2/3Sr1/3CoO8/3H2/3 based on combined Co L 23-edge absorption spectra and configuration interaction cluster calculations, from which we are able to explain the ferromagnetic ground state in terms of the distinct magnetic moment contributions from Co ions with octahedral (O h) and tetrahedral (T d) symmetries following antiparallel spin alignments. Further density functional theory calculations have been performed to verify the functionality of H+ as the transfer ion and the origin of the novel ferromagnetic insulating ground state. Our results provide a fundamental understanding of the ILG regulation mechanism and shed light on the manipulating of more functionalities in other correlated compounds through dual-ion manipulation.

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“…The σ 1 (ω) of the n = 1 and 2 SLs are qualitatively different from those of hole-doped ferromagnetic La 1-x Sr x CoO 3 crystals and thin films [22,24,27]. The latter compounds show metallic state and their ferromagnetic state is attributed to the double exchange interaction between the t 2g electrons of Co 3+ and Co 4+ ions [28][29][30]. In σ 1 (ω) spectra, the metallicity is represented by a Drude-like peak centered at zero energy.…”

Section: Optical Responsementioning

confidence: 89%

(LaCoO3)n/(SrCoO2.5)

et al. 2019

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Ferromagnetic insulators have great potential for spintronic applications. For such applications, it is essential to find materials with a robust and controllable ferromagnetic insulating phase. However, because ferromagnetism in functional transition metal oxides is usually coupled to metallicity, ferromagnetic insulators are very rare and independent control of their magnetic and electrical properties is difficult. In this study, the electrical, magnetic, and optical properties of (LaCoO 3) n /(SrCoO 2.5) n superlattice films are investigated for the manipulation of the ferromagnetic insulating phase. Whilst the superlattices remain insulating irrespective of the periodicity n, the electronic structure and magnetic state vary drastically. Superlattices with large periodicities n of 10 and 20 show a ferromagnetic transition at a critical temperature T C of ~80 K. With decreasing periodicity and increasing interface density of the superlattices, systems with n = 4 become almost nonmagnetic, while in systems with n = 2 and 1, a reentrant ferromagnetic phase is observed at T C of ~180 and ~225 K, respectively. Optical spectroscopy reveals that the fine control of the magnetic ground state is achieved by the modified electronic structure associated with the spin-state transition. Our results suggest an important design principle to create and manipulate the ferromagnetic insulating properties of Co-based oxide thin films.

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Direct observation of double exchange in ferromagneticLa0.7Sr0.3CoO3by broadband ellipsometry

Cited by 15 publications

References 30 publications

Electronic and structural properties of single-crystal Jahn–Teller active Co_1+xMn_2−xO₄ thin films

Electronic and structural properties of single-crystal Jahn–Teller active Co_1+xMn_2−xO₄ thin films

Ferromagnetic Insulating Ground-State Resolved in Mixed Protons and Oxygen Vacancies-Doped La_0.67Sr_0.33CoO₃ Thin Films via Ionic Liquid Gating

(LaCoO3)n/(SrCoO2.5)

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Direct observation of double exchange in ferromagneticLa0.7Sr0.3CoO3by broadband ellipsometry

Cited by 15 publications

References 30 publications

Electronic and structural properties of single-crystal Jahn–Teller active Co1+x Mn2−x O4 thin films

Electronic and structural properties of single-crystal Jahn–Teller active Co1+x Mn2−x O4 thin films

Ferromagnetic Insulating Ground-State Resolved in Mixed Protons and Oxygen Vacancies-Doped La0.67Sr0.33CoO3 Thin Films via Ionic Liquid Gating

(LaCoO3)n/(SrCoO2.5)

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Electronic and structural properties of single-crystal Jahn–Teller active Co_1+xMn_2−xO₄ thin films

Electronic and structural properties of single-crystal Jahn–Teller active Co_1+xMn_2−xO₄ thin films

Ferromagnetic Insulating Ground-State Resolved in Mixed Protons and Oxygen Vacancies-Doped La_0.67Sr_0.33CoO₃ Thin Films via Ionic Liquid Gating