Role of anisotropic Coulomb interactions in the superexchange coupling of mixed-valent 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Mn</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>

Yoon, Sangmoon; Lee, Sang‐Min; Pang, Subeen; Kim, Miyoung; Kwon, Young–Kyun

doi:10.1103/physrevb.104.035158

Phys. Rev. B

2021

DOI: 10.1103/physrevb.104.035158

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Role of anisotropic Coulomb interactions in the superexchange coupling of mixed-valent Mn3O4

Sangmoon Yoon

Sang‐Min Lee

Subeen Pang

et al.

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Cited by 4 publications

(1 citation statement)

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“…The role of surface reconstructions on the valence state and polar instability was further studied by analyzing the orbital configurations of Mn ions at the surfaces. The charge and orbital states of Mn ions can be directly determined by the eigenoccupation ( ) of the on-site d orbital density matrix; of surface Mn ions is summarized in Table . − To be specific, the oxidation state of each Mn ion on the surface was estimated by counting the number of occupied orbitals (i.e., the number of occupied eigenstates). The eigenorbital and eigenoccupations are fictitious auxiliary physical quantities, but they have been widely used in the analysis of orbital-dependent physical phenomena.…”

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confidence: 99%

Atomic Reconstruction and Oxygen Evolution Reaction of Mn₃O₄ Nanoparticles

Yoon

Seo

Jin

et al. 2022

J. Phys. Chem. Lett.

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Understanding the chemical states of individual surface atoms and their arrangements is essential for addressing several current issues such as catalysis, energy stroage/ conversion, and environmental protection. Here, we exploit a profile imaging technique to understand the correlation between surface atomic structures and the oxygen evolution reaction (OER) in Mn 3 O 4 nanoparticles. We image surface structures of Mn 3 O 4 nanoparticles and observe surface reconstructions in the ( 110) and ( 101) planes. Mn 3+ ions at the surface, which are commonly considered as the active sites in OER, disappear from the reconstructed planes, whereas Mn 3+ ions are still exposed at the edges of nanoparticles. Our observations suggest that surface reconstructions can deactivate low-index surfaces of Mn oxides in OER. These structural and chemical observations are further validated by density functional theory calculations. This work shows why atomic-scale characterization of surface structures is crucial for a molecular-level understanding of a chemical reaction in oxide nanoparticles.S urface chemistry and reactions are fundamental to the properties of various functional materials, including solid catalysts, supercapacitors, and sensors. 1 At the molecular level, surface atoms interact differently with surrounding molecules depending on their local atomic arrangements, such as facet, step, edge, and corner atoms, and surface defects, causing considerable variations in the chemical environment. 2 Furthermore, surface relaxation and reconstruction also significantly alter chemical reactions at the surface because of modified electronic structures. Together, surface atomic arrangements and surface reconstructions constitute what is broadly defined as surface structures. Because of the complexity of surface structures, atomic-level characterization is essential for a molecular-level understanding of surface chemical reactions. For example, identification of the active sites among various surface atoms in catalysis can lead to direct advances in catalyst design. 3 While a variety of advanced surface characterization techniques have been developed and employed to obtain information associated with chemical reactions at specific surface sites, most techniques have their own restrictions for the surface types that can be studied, and accurate measurement of atomic and electronic structures with high precision remains difficult in nanostructured materials. 4 Surface profile imaging 5,6 by transmission electron microscopy (TEM), particularly scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS), is a novel technique for the analysis of nanoparticle surfaces. The high-angle annular dark-field (HAADF) mode in STEM allows individual atomic columns to be located, and EELS provides information on the electronic and chemical states simultaneously. Recently, the capability of this technique has improved significantly due to the dramatic advances in aberration correction. Surfaces of the ...

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mentioning

confidence: 99%

Atomic Reconstruction and Oxygen Evolution Reaction of Mn₃O₄ Nanoparticles

Yoon

Seo

Jin

et al. 2022

J. Phys. Chem. Lett.

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Tunable Ferromagnetism in LaCoO₃ Epitaxial Thin Films

Shin

Yoon

Song

et al. 2022

Adv Materials Inter

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Ferromagnetic insulators play a crucial role in the development of low‐dissipation quantum magnetic devices for spintronics. Epitaxial LaCoO3 thin film is a prominent ferromagnetic insulator, in which the robust ferromagnetic ordering emerges owing to epitaxial strain. Whereas it is evident that strong spin‐lattice coupling induces ferromagnetism, the reported ferromagnetic properties of epitaxially strained LaCoO3 thin films are highly consistent. For example, even under largely modulated degree of strain, the reported Curie temperatures of epitaxially strained LaCoO3 thin films lie in a narrow range of 80–85 K, without much deviation. In this study, substantial enhancement (≈18%) in the Curie temperature of epitaxial LaCoO3 thin films is demonstrated via crystallographic orientation dependence. By changing the crystallographic orientation of the films from (111) to (110), the crystal‐field energy is reduced and the charge transfer between the Co and O orbitals is enhanced. These modifications lead to a considerable enhancement of the ferromagnetic properties (including the Curie temperature and magnetization), despite the identical nominal degree of epitaxial strain. The findings of this study provide insights into facile tunability of ferromagnetic properties via structural symmetry control in LaCoO3.

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Size Effects of Magneto-Structural Correlation in Mn₃O₄ Nanoparticles

et al. 2023

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We synthesized spinel manganese oxide Mn 3 O 4 nanoparticles with sizes ranging from 7 to 25 nm and investigated their crystal structure and magnetic properties through X-ray diffraction, magnetization, and electron spin resonance (ESR) measurements. As the particle size decreased, the lattice constant a increased monotonically, while the lattice constant c and tetragonal distortion of the unit cell reached a minimum at 11 nm and then increased rapidly below 9 nm. The ESR spectra of the nanoparticles differed from those of the bulk crystal, and the nanoparticles exhibited a hyperfine structure of Mn 2+ ions at the nanoparticle surface. The size dependence of the line width of the ESR spectrum of the nanoparticles was similar to that of the tetragonal distortion. The magnetic transition temperatures and coercive field of the nanoparticles decreased rapidly below 10 nm. The Mn 3 O 4 nanoparticles maintained three magnetic transition temperatures similar to those of bulk crystals above 9 nm. However, the nanoparticles exhibited only two distinct transition temperatures below 9 nm. Distortion of the crystal structure leads to a change in the magnetic interactions and magnetic state. It is suggested that the change of a phase boundary appears to exist at approximately 9 nm in the phase diagram of the magnetic properties as a function of the particle size.

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Role of anisotropic Coulomb interactions in the superexchange coupling of mixed-valent Mn3O4

Cited by 4 publications

References 34 publications

Atomic Reconstruction and Oxygen Evolution Reaction of Mn₃O₄ Nanoparticles

Atomic Reconstruction and Oxygen Evolution Reaction of Mn₃O₄ Nanoparticles

Tunable Ferromagnetism in LaCoO₃ Epitaxial Thin Films

Size Effects of Magneto-Structural Correlation in Mn₃O₄ Nanoparticles

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Product

Resources

About

Role of anisotropic Coulomb interactions in the superexchange coupling of mixed-valent Mn3O4

Cited by 4 publications

References 34 publications

Atomic Reconstruction and Oxygen Evolution Reaction of Mn3O4 Nanoparticles

Atomic Reconstruction and Oxygen Evolution Reaction of Mn3O4 Nanoparticles

Tunable Ferromagnetism in LaCoO3 Epitaxial Thin Films

Size Effects of Magneto-Structural Correlation in Mn3O4 Nanoparticles

Contact Info

Product

Resources

About

Atomic Reconstruction and Oxygen Evolution Reaction of Mn₃O₄ Nanoparticles

Atomic Reconstruction and Oxygen Evolution Reaction of Mn₃O₄ Nanoparticles

Tunable Ferromagnetism in LaCoO₃ Epitaxial Thin Films

Size Effects of Magneto-Structural Correlation in Mn₃O₄ Nanoparticles