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Author: Yue Jia
Publisher:
ISBN: 9780355149258
Category :
Languages : en
Pages :
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Book Description
Perovskite oxides span a diverse range of functional properties such as ferromagnetism, superconductivity, and ferroelectricity, which makes them promising candidate materials for applications such as sensors, energy conversion and data storage devices. With recent advances in thin film deposition techniques, the precise manipulation of atomic layers on the unit cell level make it possible to synthesize epitaxial thin film heterostructures consisting of layers with different properties. The structural compatibility of perovskite oxides allows them to be epitaxially grown in complex heterostructures such as superlattices with a large density of interfaces where the interplay between spin, charge, orbital, and lattice degrees of freedom gives rise to new behaviors. The ferromagnetic (FM)/antiferromagnetic (AF) interface is particularly interesting due to exchange coupling which is not only of interest for fundamental research but also is of great significance for industrial applications[superscript 1,2]. Unlike metallic systems that have been studied for decades with wide ranges of applications in devices such as hard disk drives, thin films of complex metal oxides is a relatively new field. Perovskite oxides show much more diverse functional properties than metals and open new pathways for tailoring propertiestowards specific device applications. Epitaxial La[subscript 0.7]Sr[subscript 0.3]MnO3 (LSMO)/La[subscript 0.7]Sr[subscript 0.3]FeO3 (LSFO) superlattices serve as model systems to explore the magnetic structure and exchange coupling at perovskite oxide interfaces. Earlier work suggested that (001)-oriented LSMO/LSFO superlattices with compensated AF spins at the interface display spin-flop coupling characterized by perpendicular alignment between the AF spin axes and the FM moments at a sublayer thickness of 6 unit cells (u.c.) [superscript 3-5]. Changing the crystallographic orientation of the interface from (001) to (111) introduces changes to factors such as the charge density of each stacking layer, the magnetic structure of the AF layer at the interface, the symmetry of the lattice, and the orbital degeneracy. Therefore, different properties and exchange coupling mechanisms are expected. (111)-oriented LSMO/LSFO superlattices with sublayer thicknesses ranging from 3 to 60 u.c. were synthesized and characterized. Detailed analysis of their structural, electronic, and magnetic properties were performed using synchrotron radiation based resonant x-ray reflectivity, soft x-ray magnetic spectroscopy, and photoemission electron microscopy to explore the effect of sublayer thickness on the magnetic structure and exchange coupling at (111)-oriented perovskite oxide interfaces. Interfacial effects and ultrathin superlattice sublayers can stabilize orientations of the LSFO AF spin axis which differ from that of LSFO films and LSMO/LSFO bilayers. In the ultrathin limit (3 to 6 u.c.), it was found that the AF properties of the LSFO sublayers are preserved with an out-of-plane canting of the AF spin axis, while the FM properties of the LSMO sublayers are significantly depressed. For thicker LSFO layers (> 9 u.c.), the out-of-plane canting of the AF spin axis is only present in superlattices with thick LSMO sublayers. As a result, exchange coupling in the form of spin-flop coupling exists only in superlattices which display both robust ferromagnetism and out-of-plane canting of the AF spin axis. A portion of the AF moments can be reoriented by a moderate external magnetic field through spin-flop coupling with the FM LSMO sublayers that have low magnetocrystalline anisotropy in the (111) plane. The AF order in the spin-flop coupled superlattices was studied using angle-dependent x-ray magnetic linear dichroism. The AF order can be categorized into two types: majority of the AF moments cant out-of-the-plane of the film along the 110 or 100 directions depending on the LSFO layer thickness, while a minority portion lies within the (111) plane in different AF domains. The energy difference between domains with their spin axes along the in-plane or out-of-plane directions is small, and the magnetic order of AF thin films is far more complex than in bulk LSFO. The complex AF structure in these (111)-oriented LSMO/LSFO superlattices illustrates that complex metal oxide heterostructures can serve as fertile ground for discovery of new magnetic phases, which have potential applications in next generation information technology devices.
Author: Yue Jia
Publisher:
ISBN: 9780355149258
Category :
Languages : en
Pages :
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Book Description
Perovskite oxides span a diverse range of functional properties such as ferromagnetism, superconductivity, and ferroelectricity, which makes them promising candidate materials for applications such as sensors, energy conversion and data storage devices. With recent advances in thin film deposition techniques, the precise manipulation of atomic layers on the unit cell level make it possible to synthesize epitaxial thin film heterostructures consisting of layers with different properties. The structural compatibility of perovskite oxides allows them to be epitaxially grown in complex heterostructures such as superlattices with a large density of interfaces where the interplay between spin, charge, orbital, and lattice degrees of freedom gives rise to new behaviors. The ferromagnetic (FM)/antiferromagnetic (AF) interface is particularly interesting due to exchange coupling which is not only of interest for fundamental research but also is of great significance for industrial applications[superscript 1,2]. Unlike metallic systems that have been studied for decades with wide ranges of applications in devices such as hard disk drives, thin films of complex metal oxides is a relatively new field. Perovskite oxides show much more diverse functional properties than metals and open new pathways for tailoring propertiestowards specific device applications. Epitaxial La[subscript 0.7]Sr[subscript 0.3]MnO3 (LSMO)/La[subscript 0.7]Sr[subscript 0.3]FeO3 (LSFO) superlattices serve as model systems to explore the magnetic structure and exchange coupling at perovskite oxide interfaces. Earlier work suggested that (001)-oriented LSMO/LSFO superlattices with compensated AF spins at the interface display spin-flop coupling characterized by perpendicular alignment between the AF spin axes and the FM moments at a sublayer thickness of 6 unit cells (u.c.) [superscript 3-5]. Changing the crystallographic orientation of the interface from (001) to (111) introduces changes to factors such as the charge density of each stacking layer, the magnetic structure of the AF layer at the interface, the symmetry of the lattice, and the orbital degeneracy. Therefore, different properties and exchange coupling mechanisms are expected. (111)-oriented LSMO/LSFO superlattices with sublayer thicknesses ranging from 3 to 60 u.c. were synthesized and characterized. Detailed analysis of their structural, electronic, and magnetic properties were performed using synchrotron radiation based resonant x-ray reflectivity, soft x-ray magnetic spectroscopy, and photoemission electron microscopy to explore the effect of sublayer thickness on the magnetic structure and exchange coupling at (111)-oriented perovskite oxide interfaces. Interfacial effects and ultrathin superlattice sublayers can stabilize orientations of the LSFO AF spin axis which differ from that of LSFO films and LSMO/LSFO bilayers. In the ultrathin limit (3 to 6 u.c.), it was found that the AF properties of the LSFO sublayers are preserved with an out-of-plane canting of the AF spin axis, while the FM properties of the LSMO sublayers are significantly depressed. For thicker LSFO layers (> 9 u.c.), the out-of-plane canting of the AF spin axis is only present in superlattices with thick LSMO sublayers. As a result, exchange coupling in the form of spin-flop coupling exists only in superlattices which display both robust ferromagnetism and out-of-plane canting of the AF spin axis. A portion of the AF moments can be reoriented by a moderate external magnetic field through spin-flop coupling with the FM LSMO sublayers that have low magnetocrystalline anisotropy in the (111) plane. The AF order in the spin-flop coupled superlattices was studied using angle-dependent x-ray magnetic linear dichroism. The AF order can be categorized into two types: majority of the AF moments cant out-of-the-plane of the film along the 110 or 100 directions depending on the LSFO layer thickness, while a minority portion lies within the (111) plane in different AF domains. The energy difference between domains with their spin axes along the in-plane or out-of-plane directions is small, and the magnetic order of AF thin films is far more complex than in bulk LSFO. The complex AF structure in these (111)-oriented LSMO/LSFO superlattices illustrates that complex metal oxide heterostructures can serve as fertile ground for discovery of new magnetic phases, which have potential applications in next generation information technology devices.
Author: Bakshi Venugopal Rao
Publisher: Mohammed Abdul Malik
ISBN:
Category : Science
Languages : en
Pages : 0
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Book Description
Perovskite materials with a general formula ABO3 exhibit rich and varying physical properties including magnetic, semi-conducting, ferroelectric, multiferroic. Thus it is interesting and meaningful in both theory and experiments of these materials. In ABO3 structure, the zero occupancy of the transition metal B cations are chemically known to favour ferroelectricity. The availability of the transition metal d electrons in the perovskite oxides are necessary for magnetism to reduce the tendency for off centering ferroelectric distortions. Hence ferromagnetism and ferroelectricity seem to be mutually exclusive in perovskite structure oxides and the scarcity of ferromagnetic and ferroelectric materials has stimulated many theoretical and experimental works. A few metal oxides are known to exhibit ferroelectricity at relatively high temperatures and a magnetic transition at lower temperatures. Recently some researchers have found that rare earth chromites with formula ReCrO3 exhibit canted anti ferromagnetic [TN=113-140 K] and dielectric [TC=472-516K] transition characteristic which is a kind of possible multiferroic behavior. From the above discussion it is clear that the importance of the perovskite structure which has a stable and standard structure and also the transition metal oxides as a possible important application as a multiferroic materials. In particular, the rare earth transition metal oxides from the perovskite family are well known due to their striking properties which are related to exchange mechanisms and the competition between ferromagnetic and anti-ferromagnetic phases
Author: Gibin George
Publisher: CRC Press
ISBN: 1000195724
Category : Technology & Engineering
Languages : en
Pages : 404
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Book Description
This textbook entitled Fundamentals of Perovskite Oxides: Synthesis, Structure, Properties and Applications summarizes the structure, synthesis routes, and potential applications of perovskite oxide materials. Since these perovskite-type ceramic materials offer opportunities in a wide range of fields of science and engineering, the chapters are broadly organized into four sections of perovskite-type oxide materials and technology. Covers recent developments in perovskite oxides Serves as a quick reference of perovskite oxides information Describes novel synthesis routes for nanostructured perovskites Discusses comprehensive details for various crystal structures, synthesis methods, properties, and applications Applies to academic education, scientific research, and industrial R&D for materials research in real-world applications like bioengineering, catalysis, energy conversion, energy storage, environmental engineering, and data storage and sensing This book serves as a handy and practical guideline suitable for students, engineers, and researchers working with advanced ceramic materials.
Author: Likun Pan
Publisher:
ISBN: 9789535166511
Category : Oracle Applications
Languages : en
Pages : 0
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Book Description
Author: Asish K Kundu
Publisher: Springer
ISBN: 8132227611
Category : Technology & Engineering
Languages : en
Pages : 174
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Book Description
Magnetic perovskite with multi functional properties (magneto-resistive, magneto-dielectric, multiferroics, spintronics, etc.) have attracted increasing attention due to their possible applications towards storage materials and intriguing fundamental Physics. Despite the numerous investigations on multi functional materials in the past few years, a very few magnetic perovskites have been known to realize as ferromagnetic-insulators. In perovskites centred transition metal oxides strong interplay between lattice, charge, spin and/or orbital degrees of freedom provide a fantastic playground to tune their physical properties. The main purpose of this book is to introduce the phenomenon and physics of complex magnetism (phase separation, spin glass, frustrations, etc.) in perovskite manganites and cobaltites via an experimental approach. The book is organized into four chapters; Chap. 1 gives a brief introduction of various interesting phenomena in magnetic perovskites. Chapter 2 describes the results of the investigations on electronic phase separation and glassy ferromagnetism of the hole-doped perovskite manganites and cobaltites. Ordered and disordered effects and related aspects in hole-doped perovskite cobaltites are described in Chap. 3. Finally, in Chap. 4 the bismuth based magnetic perovskite is discussed.
Author: Bekir Aktas
Publisher: Springer Science & Business Media
ISBN: 3642349587
Category : Science
Languages : en
Pages : 229
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Book Description
This book provides an up-to-date review of nanometer-scale magnetism and focuses on the investigation of the basic properties of magnetic nanostructures. It describes a wide range of physical aspects together with theoretical and experimental methods. A broad overview of the latest developments in this emerging and fascinating field of nanostructured materials is given with emphasis on the practical understanding and operation of submicron devices based on nanostructured magnetic materials.
Author: Andrew Izumi
Publisher:
ISBN: 9781339260808
Category :
Languages : en
Pages :
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Book Description
Studies into a class of materials known as complex oxides have evoked a great deal of interest due to their unique magnetic, ferroelectric, and superconducting properties. In particular, materials with the ABO3 perovskite structure have highly tunable properties because of the high stability of the structure, which allows for large scale doping and strain. This also allows for a large selection of A and B cations and valences, which can further modify the material's electronic structure. Additionally, deposition of these materials as thin films and superlattices through techniques such as pulsed laser deposition (PLD) results in novel properties due to the reduced dimensionality of the material. The novel properties of perovskite oxide heterostructures can be traced to a several sources, including chemical intermixing, strain and defect formation, and electronic reconstruction. The correlations between microstructure and physical properties must be investigated by examining the physical and electronic structure of perovskites in order to understand this class of materials. Some perovskites can undergo phase changes due to temperature, electrical fields, and magnetic fields. In this work we investigated Nd0.5Sr0.5MnO3 (NSMO), which undergoes a first order magnetic and electronic transition at T=158K in bulk form. Above this temperature NSMO is a ferromagnetic metal, but transitions into an antiferromagnetic insulator as the temperature is decreased. This rapid transition has interesting potential in memory devices. However, when NSMO is deposited on (001)-oriented SrTiO3 (STO) or (001)-oriented (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) substrates, this transition is lost. It has has been reported in the literature that depositing NSMO on (110)-oriented STO allows for the transition to reemerge due to the partial epitaxial growth, where the NSMO film is strained along the [001] surface axis and partially relaxed along the [11̄0] surface axis. This allows the NSMO film enough freedom of movement to undergo a shear strain along the [11̄0] axes, allowing the NSMO film to switch phases. It was found that the desired magnetic and electrical properties were closely tied to the structural properties, which were highly sensitive to the precise growth conditions. These perovskite oxides can be further geometrically constrained by patterning, resulting in additional novel magnetic and electrical properties. One such method of patterning involves implanting Ar into a film to locally destabilize the ordered perovskite structure, therefore suppress the magnetic and electrical properties. However, to fully integrate this technique into devices which require multi-planar processes, the ability for a patterned perovskite film to withstand high temperature anneals is crucial in creating more advanced structures. The stability of Ar-implanted La0.7Sr0.3MnO3 (LSMO) thin films was studied upon annealing at 400°C, 500°C, and 600°C. The LSMO retained its amorphous structure with little ferromagnetism after a 400°C anneal, but anneals at 500°C and 600°C resulted in partial recrystallization and a return of the ferromagnetic properties. This recrystallized film displayed semiconducting properties with a lower Curie temperature than the as deposited film. The deposition of an La0.7Sr0.3FeO3 (LSFO) film onto an Ar implanted LSMO film at 400°C caused the LSMO film to almost fully recrystallize, suggesting that the deposition process also recrystallizes the Ar-implanted film. In conclusion, two perovskites films were explored in this thesis. NSMO films proved to be very sensitive to growth conditions, and Ar-implanted LSMO films quickly recrystallized past 400°C or a subsequent film deposition. These studies provide useful information on the structural and electronic transformations these films go through during heat treatment and strain engineering.
Author: Jason Lapano
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The three core tenants of materials science are theory, synthesis, and characterization. A solid theoretical framework is required for understanding of the problem at hand and using that knowledge to advance new areas of research. Synthesis of pristine materials is required to study the theory in a physical system and prevent misinterpretation of results. Complex structures and compositions are often the most interesting, and when defects and impurities are of interest, perfectly-imperfect samples are required which are often the most challenging to synthesize. Characterization of these materials is equally as important and complex, requiring careful sample preparation and experimental setups. Further, it is not always clear how to observe the property of scientific interest, and new characterization techniques must be developed. This dissertation focuses on using these three tenants to understand and advance the field of transition metal perovskite complex oxides using thin films of the incipient ferroelectrics CaTiO3 and SrTiO3 and antiferromagnetic Mott-Insulators LaVO3 and YVO3. The knowledge gained in this thesis can be applied to other complex oxide materials in better understanding magnetic and electronic transitions, high Tc superconductivity and quantum hall effect. Coupled with the relatively simple structure and ease of integration of multiple different chemical compounds into a single heterostructure leads to near numerous avenues to design functionality into materials.The first sections of this thesis begin with (1) an introduction to the basic science and past work in perovskite oxides, followed by (2) exploring the most common and promising synthesis routes, and finally (3) the various characterization methods used. The 4th chapter addresses the specific challenges of growth of ternary complex oxide thin films in an industrially profitable fashion. The three primary criterion that these deposition methods must adhere to is that they must (a) control film stoichiometry to less than 1% deviations, (b) deposit conformal coatings over standard 8 silicon wafers, (c) and exhibit deposition rates in excess of 1 m/hr. We show that these can be achieved using a hybrid molecular beam (hMBE) epitaxy approach and outline a route for commercially viable growth of complex oxides on silicon. This method is applied directly to the deposition of SrTiO3 on silicon for virtual single crystal perovskite substrates. The 5th chapter of this thesis discusses the effect of epitaxial strain, stoichiometry and interfacial coupling in heterostructures of complex oxides. In the (SrTiO3)n(CaTiO3)n series of superlattices grown by hMBE, it is found that interfacial energies play a large role in dictating the macroscopic properties, particularly ferroelectricity. In coherently strained thin films, both CaTiO3 and SrTiO3 exhibit relaxor-like ferroelectric behavior below room temperature. However, certain superlattices of these materials show nonpolar behavior when probed using second harmonic generation (SHG). High resolution scanning transmission electron microscopy (STEM) reveals that the symmetry in the superlattice is different from the individual parent compounds at the same strain state. It is found these are directly related to the high density of interfacial layers present in the films. Further, interfacial mixing of the constituent layers on certain superlattices leads to the development of a Ca1-xSrxTiO3 alloy which develops a ferroelectric moment at low temperatures, leading to spurious SHG signals. The findings of this experiment highlight the sensitivity of these complex layered structures to strain, stoichiometry, distortion coupling effects, and interfacial mixing.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
We investigate the structural, magnetic, and electrical properties of superlattices composed of the ferromagnetic/metal La0.7Sr0.3MnO3 and non-magnetic/metal La0.5Sr0.5TiO3 grown on (001)-oriented SrTiO3 substrates. Using a combination of bulk magnetometry, soft x-ray magnetic spectroscopy, and scanning transmission electron microscopy, we demonstrate that robust ferromagnetic properties can be maintained in this superlattice system where charge transfer at the interfaces is minimized. Thus, ferromagnetism can be controlled effectively through the chemical identity and the thickness of the individual superlattice layers.
Author: Heng Wu
Publisher:
ISBN:
Category : Technology
Languages : en
Pages :
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Book Description
Perovskite oxide nanocrystals exhibit a wide spectrum of attractive properties such as ferroelectricity, piezoelectricity, dielectricity, ferromagnetism, magnetoresistance, and multiferroics. These properties are indispensable for applications in ferroelectric random access memories, multilayer ceramic capacitors, transducers, sensors and actuators, magnetic random access memories, and the potential new types of multiple-state memories and spintronic devices controlled by electric and magnetic fields. In the past two decades, much effort has been made to synthesize and characterize the perovskite oxide nanocrystals. Various physical and chemical deposition techniques and growth mechanisms are explored and developed to control the morphology, identical shape, uniform size, perfect crystalline structure, defects, and homogenous stoichiometry of the perovskite oxide nanocrystals. This chapter provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, structural characterization, functionalization, and unique applications of perovskite oxide nanocrystals in nanoelectronics. It begins with the rational synthesis of perovskite oxide nanocrystals, and then summarizes their structural characterizations. Fundamental physical properties of perovskite oxide nanocrystals are also highlighted, and a range of novel applications in nanoelectronics, information storages, and spintronics are discussed. Finally, we conclude this review with some perspectives/outlook and future researches in these fields.
