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Journal ArticleDOI

Ferromagnetism in metal oxide systems: interfaces, dopants, and defects

31 Jan 2013-Journal of Materials Chemistry C (The Royal Society of Chemistry)-Vol. 1, Iss: 8, pp 1545-1557
TL;DR: A review of the developments in this field by late 2011 and 2012 can be found in this paper, where a number of techniques are applied to bring out materials issues that are critical to the precise understanding of the origin of magnetism in certain cases.
Abstract: Ferromagnetism in metal oxide systems has always attracted scientific attention in view of the intriguing and interesting interplay of spin, charge, orbital and lattice degrees of freedom that such systems display. This trend appears to be continuing with enhanced focus on interface systems, multiferroics, diluted magnetic semiconducting oxides (DMSOs) and nanomaterial magnetism. Newer techniques are being applied to bring out materials issues that are critical to the precise understanding of the origin of magnetism in certain cases. Interest is also beginning to grow in exploring application potential of some such systems. In this article we review the developments in this field by late 2011 and 2012.
Citations
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Journal ArticleDOI
Feng Pan1, Song Gao1, Chao Chen1, Cheng Song1, Fei Zeng1 
TL;DR: A comprehensive review of the recent progress in the so-called resistive random access memories (RRAMs) can be found in this article, where a brief introduction is presented to describe the construction and development of RRAMs, their potential for broad applications in the fields of nonvolatile memory, unconventional computing and logic devices, and the focus of research concerning RRAMS over the past decade.
Abstract: This review article attempts to provide a comprehensive review of the recent progress in the so-called resistive random access memories (RRAMs) First, a brief introduction is presented to describe the construction and development of RRAMs, their potential for broad applications in the fields of nonvolatile memory, unconventional computing and logic devices, and the focus of research concerning RRAMs over the past decade Second, both inorganic and organic materials used in RRAMs are summarized, and their respective advantages and shortcomings are discussed Third, the important switching mechanisms are discussed in depth and are classified into ion migration, charge trapping/de-trapping, thermochemical reaction, exclusive mechanisms in inorganics, and exclusive mechanisms in organics Fourth, attention is given to the application of RRAMs for data storage, including their current performance, methods for performance enhancement, sneak-path issue and possible solutions, and demonstrations of 2-D and 3-D crossbar arrays Fifth, prospective applications of RRAMs in unconventional computing, as well as logic devices and multi-functionalization of RRAMs, are comprehensively summarized and thoroughly discussed The present review article ends with a short discussion concerning the challenges and future prospects of the RRAMs

1,129 citations

Journal ArticleDOI
Kelan Yan1, Runhua Fan1, Zhicheng Shi1, Min Chen1, Lei Qian1, Yu-lei Wei1, Kai Sun1, Jing Li1 
TL;DR: In this article, an interesting negative permittivity behavior of single-phase perovskite La1−xSrxMnO3 (LSMO) was found, where the LSMO bulks with an x value of 0.2 or 0.5 were prepared by a solgel/sintering process.
Abstract: For double negative materials (DNMs), these are usually observed in artificial metamaterials or some metal/ceramic composites. Here, an interesting negative permittivity behavior of single-phase perovskite La1−xSrxMnO3 (LSMO) is found. The LSMO bulks with an x value of 0.2 or 0.5 were prepared by a sol–gel/sintering process. From microstructure characterization, the bulks are nearly in single phase and the major phase belongs to the perovskite structure; meanwhile, the bulks are of high density. Furthermore, the experimental data of the plasma-like negative permittivity are fitted well by a lossy Drude model, suggesting a plasma frequency of 3.85 GHz (x = 0.5). The complex permeability of LSMO presents a negative susceptibility (μ′ < 1) at a frequency range of 0.2–1 GHz (x = 0.2) and 0.6–1 GHz (x = 0.5). These results have important implications for the realization of double negative properties in single-phase LSMO as a promising candidate for DNMs.

86 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of annealing on structural defects and d(0) ferromagnetism in SnO2 nanoparticles prepared by solution combustion method is investigated.
Abstract: The effect of annealing on structural defects and d(0) ferromagnetism in SnO2 nanoparticles prepared by solution combustion method is investigated. The as-synthesized SnO2 nanoparticles were annealed at 400-800 degrees C for 2 h, in ambient conditions. The crystallinity, size, and morphology of the samples were studied using x-ray diffraction and transmission electron microscopy studies. The annealing results in grain growth due to coarsening as well as reduction in oxygen vacancies as confirmed by Raman spectroscopy, photoluminescence spectroscopy, and x-ray photoelectron spectroscopy. All the as synthesized and annealed samples exhibit room temperature ferromagnetism (RTFM) with distinct hysteresis loops and the saturation magnetization as high as similar to 0.02 emu/g in as-synthesized samples. However, the saturation magnetization is drastically reduced with increasing annealing temperature. Further the presence of singly charged oxygen vacancies (V-o(-) signal at g-value 1.99) is confirmed by electron paramagnetic resonance studies, which also diminish with increasing annealing temperature. The observed diminishing RTFM and simultaneous evidences of diminishing O vacancies clearly indicate that RTFM is driven by defects in oxide lattice and confirms primary role of oxygen vacancies in inducing ferromagnetic ordering in metal oxide semiconductors. The study also provides improved fundamental understanding regarding the ambiguity in the origin of intrinsic RTFM in semiconducting metal oxides and projects their technological application in the field of spintronics. (C) 2013 AIP Publishing LLC.

78 citations

Journal ArticleDOI
TL;DR: In this article, the gas sensing properties of Al-doped ZnO thin films have been reported where the nanocrystalline znO based thin films were well deposited by a simple and inexpensive chemical spray pyrolysis (CSP) technique.

73 citations

Journal ArticleDOI
TL;DR: The structural, optical, magnetic, and electrical properties of sol-gel-derived Ti1−xFexO2 (0.00 ≤ x ≤ 0.05) nanoparticles were investigated in this paper.
Abstract: The structural, optical, magnetic, and electrical properties of sol–gel-derived Ti1−xFexO2 (0.00 ≤ x ≤ 0.05) nanoparticles were investigated. Rietveld refinement of the X-ray diffraction data and TEM measurements were carried out to analyze the crystalline structure and quality of all the samples. Raman spectroscopy revealed a decrease in intensity and broadening of the characteristics peaks of Fe-doped TiO2 with respect to those of the pristine sample, which signifies a structural distortion of the lattices. FT-IR, UV-vis, and PL spectroscopy were used to investigate the optical properties. Magnetic measurements showed a weak ferromagnetism at room temperature in both the pristine and Fe-doped TiO2 (x = 0, 0.02, and 0.05) nanoparticles. Temperature-dependent resistivity measurements showed the semiconducting nature of the samples and revealed that the thermally activated conduction (Arrhenius) mechanism is valid in the high-temperature region, whereas Mott variable range hopping (VRH) mechanism is valid in the low-temperature region. Dielectric properties of the samples were studied as a function of temperature in the frequency range of 1 kHz to 1 MHz.

68 citations

References
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Journal ArticleDOI
TL;DR: A review of the metal-insulator transition can be found in this article, where a pedagogical introduction to the subject is given, as well as a comparison between experimental results and theoretical achievements.
Abstract: Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and $t\ensuremath{-}J$ models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in $d$-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and orbital fluctuations, mass renormalization effects, incoherence of charge dynamics, and phase transitions under control of key parameters such as band filling, bandwidth, and dimensionality. These parameters are experimentally varied by doping, pressure, chemical composition, and magnetic fields. Much of the observed behavior can be described by the current theory. Open questions and future problems are also extracted from comparison between experimental results and theoretical achievements.

5,781 citations

Journal ArticleDOI
29 Jan 2004-Nature
TL;DR: A model interface is examined between two insulating perovskite oxides—LaAlO3 and SrTiO3—in which the termination layer at the interface is controlled on an atomic scale, presenting a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.
Abstract: Polarity discontinuities at the interfaces between different crystalline materials (heterointerfaces) can lead to nontrivial local atomic and electronic structure, owing to the presence of dangling bonds and incomplete atomic coordinations. These discontinuities often arise in naturally layered oxide structures, such as the superconducting copper oxides and ferroelectric titanates, as well as in artificial thin film oxide heterostructures such as manganite tunnel junctions. If polarity discontinuities can be atomically controlled, unusual charge states that are inaccessible in bulk materials could be realized. Here we have examined a model interface between two insulating perovskite oxides--LaAlO3 and SrTiO3--in which we control the termination layer at the interface on an atomic scale. In the simple ionic limit, this interface presents an extra half electron or hole per two-dimensional unit cell, depending on the structure of the interface. The hole-doped interface is found to be insulating, whereas the electron-doped interface is conducting, with extremely high carrier mobility exceeding 10,000 cm2 V(-1) s(-1). At low temperature, dramatic magnetoresistance oscillations periodic with the inverse magnetic field are observed, indicating quantum transport. These results present a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.

3,977 citations

Journal ArticleDOI
TL;DR: Novel device paradigms based on magnetoelectric coupling are discussed, the key scientific challenges in the field are outlined, and high-quality thin-film multiferroics are reviewed.
Abstract: Multiferroic materials, which show simultaneous ferroelectric and magnetic ordering, exhibit unusual physical properties — and in turn promise new device applications — as a result of the coupling between their dual order parameters. We review recent progress in the growth, characterization and understanding of thin-film multiferroics. The availability of high-quality thin-film multiferroics makes it easier to tailor their properties through epitaxial strain, atomic-level engineering of chemistry and interfacial coupling, and is a prerequisite for their incorporation into practical devices. We discuss novel device paradigms based on magnetoelectric coupling, and outline the key scientific challenges in the field.

3,472 citations

Journal ArticleDOI
TL;DR: In this paper, a large variety of experiments reviewed in detail here contain results compatible with the theoretical predictions, including phase diagrams of manganite models, the stabilization of the charge/orbital/spin ordered half-doped correlated electronics (CE)-states, the importance of the naively small Heisenberg coupling among localized spins, the setup of accurate mean-field approximations, and the existence of a new temperature scale T∗ where clusters start forming above the Curie temperature, the presence of stripes in the system, and many others.

2,927 citations

Journal ArticleDOI
31 Aug 2007-Science
TL;DR: This work reports on superconductivity in the electron gas formed at the interface between two insulating dielectric perovskite oxides, LaAlO3 and SrTiO3.
Abstract: At interfaces between complex oxides, electronic systems with unusual electronic properties can be generated. We report on superconductivity in the electron gas formed at the interface between two insulating dielectric perovskite oxides, LaAlO3 and SrTiO3. The behavior of the electron gas is that of a two-dimensional superconductor, confined to a thin sheet at the interface. The superconducting transition temperature of ≅ 200 millikelvin provides a strict upper limit to the thickness of the superconducting layer of ≅ 10 nanometers.

2,317 citations