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Sharma V, Pal S, Sharma D, Shukla DK, Chaudhary RJ, Okram GS. Size-induced exchange bias in single-phase CoO nanoparticles. NANOTECHNOLOGY 2024; 35:275702. [PMID: 38635294 DOI: 10.1088/1361-6528/ad3256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Accepted: 03/10/2024] [Indexed: 04/19/2024]
Abstract
The tuning of exchange bias (EB) in nanoparticles has garnered significant attention due to its diverse range of applications. Here, we demonstrate EB in single-phase CoO nanoparticles, where two magnetic phases naturally emerge as the crystallite size decreases from 34.6 ± 0.8 to 10.8 ± 0.9 nm. The Néel temperature (TN) associated with antiferromagnetic ordering decreases monotonically with the reduction in crystallite size, highlighting the significant influence of size effects. The 34.6 nm nanoparticles exhibit magnetization irreversibility between zero-field cooled (ZFC) and field-cooled (FC) states belowTN. With further reduction in size this irreversibility appears well aboveTN, resulting in the absence of true paramagnetic regime which indicates the occurnace of an additional magnetic phase. The frequency-dependent ac-susceptibility in 10.8 nm nanoparticles suggests slow dynamics of disordered surface spins aboveTN, coinciding with the establishment of long-range order in the core. The thermoremanent magnetization (TRM) and iso-thermoremanent magnetization (IRM) curves suggest a core-shell structure: the core is antiferromagnetic, and the shell consists of disordered surface spins causing ferromagnetic interaction. Hence, the EB in these CoO nanoparticles results from the exchange coupling between an antiferromagnetic core and a disordered shell that exhibits unconventional surface spin characteristics.
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Affiliation(s)
- Vikash Sharma
- UGC-DAE Consortium for Scientific Research University campus, Khandwa road, Indore-452001, Madhya Pradesh, India
| | - Sudip Pal
- UGC-DAE Consortium for Scientific Research University campus, Khandwa road, Indore-452001, Madhya Pradesh, India
| | - Divya Sharma
- Govt. Girls PG College, Ujjain-456010, MP, India
| | - Dinesh Kumar Shukla
- UGC-DAE Consortium for Scientific Research University campus, Khandwa road, Indore-452001, Madhya Pradesh, India
| | - Ram Janay Chaudhary
- UGC-DAE Consortium for Scientific Research University campus, Khandwa road, Indore-452001, Madhya Pradesh, India
| | - Gunadhor Singh Okram
- UGC-DAE Consortium for Scientific Research University campus, Khandwa road, Indore-452001, Madhya Pradesh, India
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2
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Gómez-Toledo M, López-Paz SA, García-Martín S, Arroyo-de Dompablo ME. Metal-to-Insulating Transition in the Perovskite System YSr 2Cu 2FeO 8-δ (0 < δ < 1) Modeled by DFT Methods. Inorg Chem 2023; 62:3445-3456. [PMID: 36787462 PMCID: PMC9976288 DOI: 10.1021/acs.inorgchem.2c03475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
Progress in the design of functional perovskite oxides relies on advances in density functional theory (DFT) methods to efficiently and effectively model complex systems composed of several transition-metal ions. This work reports the application of DFT methods to investigate the electronic structure of the YSr2Cu2FeO8-δ (0 < δ < 1) family in which the insulating, metal, or superconducting behaviors and even anion conductivity can be tuned by modifying the oxygen content. In particular, we assess the performance of the generalized gradient approximation (GGA), its Hubbard-U correction (GGA + U), and the strongly constrained and appropriately normed (SCAN) to model the metallic (idealized YSr2Cu2FeO8) and insulating (idealized YSr2Cu2FeO7) phases of the system. The analysis of the DFT results is supported by DC resistivity measurements that denote the metal character of the synthesized YSr2Cu2FeO7.86 and the semiconducting character of YSr2Cu2FeO7.08 prepared under reducing conditions. In addition, the band gap of YSr2Cu2FeO7.08, in the range of 0.73-1.2 eV, has been extracted from diffuse reflectance spectroscopy (DRS). While the three methodologies (GGA, GGA + U, SCAN) permit the reproduction of the crystal structures of the synthetized oxides (determined here in the case of YSr2Cu2FeO7.08 by neutron powder diffraction (NPD)), the SCAN emerges as the only one capable to predict the basic electronic and magnetic properties across the YSr2Cu2FeO8-δ (0 < δ < 1) series. The picture that emerges for the metal (δ = 0) to insulating (δ = 1) transition is the one in which oxygen vacancies contribute electrons to the filling of the Cu/Fe-3dx2-y2 states of the conduction band. These results validate the SCAN functional for future DFT investigations of complex functional oxides that combine several transition metals.
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Affiliation(s)
- Marianela Gómez-Toledo
- Departamento
de Química Inorgánica, Universidad
Complutense de Madrid, 28040 Madrid, Spain
| | - Sara A. López-Paz
- Departamento
de Química Inorgánica, Universidad
Complutense de Madrid, 28040 Madrid, Spain,Department
of Quantum Matter Physics, University of
Geneva, CH-1211 Geneva, Switzerland
| | - Susana García-Martín
- Departamento
de Química Inorgánica, Universidad
Complutense de Madrid, 28040 Madrid, Spain
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3
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Jena S, Datta S. Evidence of half-metallicity at the BiFeO 3(001) surface. NEW J CHEM 2023. [DOI: 10.1039/d2nj06169d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/05/2023]
Abstract
Evidence of half-metallicity at the BiFeO3 (001) surface has been found. Half-metals are considered to be one of the most promising candidate for efficient spin-injection and detection processes in spintronic devices.
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Affiliation(s)
- Soumyasree Jena
- Department of Physics and Astronomy, National Institute of Technology, Rourkela, Odisha, 769008, India
| | - Sanjoy Datta
- Department of Physics and Astronomy, National Institute of Technology, Rourkela, Odisha, 769008, India
- Center for Nanomaterials, National Institute of Technology, Rourkela, Odisha, 769008, India
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Jana S, Patra A, Constantin LA, Samal P. Screened range-separated hybrid by balancing the compact and slowly varying density regimes: Satisfaction of local density linear response. J Chem Phys 2020; 152:044111. [PMID: 32007058 DOI: 10.1063/1.5131530] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Due to their quantitative accuracy and ability to solve several difficulties, screened range-separated hybrid exchange-correlation functionals are now a standard approach for ab initio simulation of condensed matter systems. However, the screened range-separated hybrid functionals proposed so far are biased either toward compact or slowly varying densities. In this paper, we propose a screened range-separated hybrid functional, named HSEint, which can well describe these density regimes, achieving good accuracy for both molecular and solid-state systems. The semilocal part of the proposed functional is based on the PBEint generalized gradient approximation [E. Fabiano et al., Phys. Rev. B 82, 113104 (2010)], constructed for hybrid interfaces. To improve the functional performance, we employ exact or nearly exact constraints in the construction of range-separated hybrid functional, such as recovering of the local density linear response and semiclassical atom linear response.
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Affiliation(s)
- Subrata Jana
- School of Physical Sciences, National Institute of Science Education and Research, HBNI, Bhubaneswar 752050, India
| | - Abhilash Patra
- School of Physical Sciences, National Institute of Science Education and Research, HBNI, Bhubaneswar 752050, India
| | - Lucian A Constantin
- Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, Via Barsanti, I-73010 Arnesano, Italy
| | - Prasanjit Samal
- School of Physical Sciences, National Institute of Science Education and Research, HBNI, Bhubaneswar 752050, India
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Herklotz A, Lee D, Guo EJ, Meyer TL, Petrie JR, Lee HN. Strain coupling of oxygen non-stoichiometry in perovskite thin films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:493001. [PMID: 29130456 DOI: 10.1088/1361-648x/aa949b] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The effects of strain and oxygen vacancies on perovskite thin films have been studied in great detail over the past decades and have been treated separately from each other. While epitaxial strain has been realized as a tuning knob to tailor the functional properties of correlated oxides, oxygen vacancies are usually regarded as undesirable and detrimental. In transition metal oxides, oxygen defects strongly modify the properties and functionalities via changes in oxidation states of the transition metals. However, such coupling is not well understood in epitaxial films, but rather deemed as cumbersome or experimental artifact. Only recently it has been recognized that lattice strain and oxygen non-stoichiometry are strongly correlated in a vast number of perovskite systems and that this coupling can be beneficial for information and energy technologies. Recent experimental and theoretical studies have focused on understanding the correlated phenomena between strain and oxygen vacancies for a wide range of perovskite systems. These correlations not only include the direct relationship between elastic strain and the formation energy of oxygen vacancies, but also comprise highly complex interactions such as strain-induced phase transitions due to oxygen vacancy ordering. Therefore, we aim in this review to give a comprehensive overview on the coupling between strain and oxygen vacancies in perovskite oxides and point out the potential applications of the emergent functionalities strongly coupled to oxygen vacancies.
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Affiliation(s)
- Andreas Herklotz
- Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
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Fischer G, Sanchez N, Adeagbo W, Szotek Z, Temmerman WM, Ernst A, Hoffmann M, Hergert W, Muñoz MC. Ab initio study of the p-hole magnetism at polar surfaces of ZnO: the role of correlations. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:016003. [PMID: 26657257 DOI: 10.1088/0953-8984/28/1/016003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A standard local density approximation and its self-interaction corrected version are applied to study spontaneous magnetization, promoted by localized p electron holes, of polar oxygen-terminated ZnO surfaces. The electronic properties and magnetic exchange interactions of three different facets are calculated. It is demonstrated that partially filled oxygen p orbitals of the polar surfaces exhibit magnetic moment formation and long range magnetic order leading to the occurrence of a ferromagnetic ground state. Monte Carlo simulations predict Curie temperatures above room temperature. In contrast to isolated defects in bulk materials, applying correlation corrections to the localized p-like surface states does not lead to a collapse of magnetic interaction: as the weakening of the magnetic interaction, caused by the reduced electronic overlap, is compensated by a strengthening due to an increase of the magnetic moments, the ferromagnetism can principally persist above room temperature, provided a large hole concentration exists.
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Affiliation(s)
- Guntram Fischer
- Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany
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Tyunina M, Chvostova D, Pacherova O, Kocourek T, Jelinek M, Jastrabik L, Dejneka A. Ambience-sensitive optical refraction in ferroelectric nanofilms of NaNbO 3. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2014; 15:045001. [PMID: 27877702 PMCID: PMC5090690 DOI: 10.1088/1468-6996/15/4/045001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Revised: 07/02/2014] [Accepted: 06/15/2014] [Indexed: 06/06/2023]
Abstract
Optical index of refraction n is studied by spectroscopic ellipsometry in epitaxial nanofilms of NaNbO3 with thickness ∼10 nm grown on different single-crystal substrates. The index n in the transparency spectral range (n ≈ 2.1 - 2.2) exhibits a strong sensitivity to atmospheric-pressure gas ambience. The index n in air exceeds that in an oxygen ambience by δn ≈ 0.05 - 0.2. The thermo-optical behaviour n(T) indicates ferroelectric state in the nanofilms. The ambience-sensitive optical refraction is discussed in terms of fundamental connection between refraction and ferroelectric polarization in perovskites, screening of depolarizing field on surfaces of the nanofilms, and thermodynamically stable surface reconstructions of NaNbO3.
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Affiliation(s)
- Marina Tyunina
- Microelectronics and Materials Physics Laboratories, University of Oulu, PO Box 4500, FI-90014 Oulun yliopisto, Finland
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
| | - Dagmar Chvostova
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
| | - Oliva Pacherova
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
| | - Tomas Kocourek
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
| | - Miroslav Jelinek
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
| | - Lubomir Jastrabik
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
| | - Alexander Dejneka
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
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Bristowe NC, Ghosez P, Littlewood PB, Artacho E. The origin of two-dimensional electron gases at oxide interfaces: insights from theory. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:143201. [PMID: 24637267 DOI: 10.1088/0953-8984/26/14/143201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The response of oxide thin films to polar discontinuities at interfaces and surfaces has generated enormous activity due to the variety of interesting effects that it gives rise to. A case in point is the discovery of the electron gas at the interface between LaAlO3 and SrTiO3, which has since been shown to be quasi-two-dimensional, switchable, magnetic and/or superconducting. Despite these findings, the origin of the two-dimensional electron gas is highly debated and several possible mechanisms remain. Here we review the main proposed mechanisms and attempt to model expected effects in a quantitative way with the ambition of better constraining what effects can/cannot explain the observed phenomenology. We do it in the framework of a phenomenological model constructed to provide an understanding of the electronic and/or redox screening of the chemical charge in oxide heterostructures. We also discuss the effect of intermixing, both conserving and not conserving the total stoichiometry.
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Affiliation(s)
- N C Bristowe
- Theoretical Materials Physics, University of Liège, B-4000 Sart-Tilman, Belgium. Theory of Condensed Matter, Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK
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