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Articles de revues sur le sujet "Novel Crystal Structure - Transition Metal Oxides - Magnetic Properties"
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Dabić, Predrag, Volker Kahlenberg, Biljana Krüger, Marko Rodić, Sabina Kovač, Jovan Blanuša, Zvonko Jagličić, Ljiljana Karanović, Václav Petříček et Aleksandar Kremenović. « Low-temperature phase transition and magnetic properties of K3YbSi2O7 ». Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 77, no 4 (23 juillet 2021) : 584–93. http://dx.doi.org/10.1107/s2052520621006077.
Texte intégralRésumé :
The new ambient-temperature hexagonal (space group P63 /mmc) polymorph of tripotassium ytterbium(III) disilicate (β-K3YbSi2O7) has been synthesized by the high-temperature flux method and subsequently structurally characterized. In the course of the temperature-dependent single-crystal diffraction experiments, a phase transformation of β-K3YbSi2O7 to a novel low-temperature orthorhombic phase (β′-K3YbSi2O7, space group Cmcm) has been observed at about 210 K. β-K3YbSi2O7 is isostructural with K3ErSi2O7, whereas β′-K3YbSi2O7 adopts a new type of structure. Both compounds can be built up from a regular alternation of layers of two types, which are parallel to the (001) plane. In the octahedral layer, YbO6 octahedra are isolated and linked by K1O6+3 polyhedra. The second, slightly thicker sorosilicate layer is formed by a combination of Si2O7 dimers and K2O6+3 polyhedra. The boundary between the layers is a pseudo-kagome oxide sheet based on 3.6.3.6 meshes. The phase transition is due to a tilt of the two SiO4 tetrahedra forming a single dimer which induces a decrease of the Si—O—Si angle between bridging Si—O bonds from 180° (dictated by symmetry in space group P63/mmc) to ≃164°. Magnetic characterization indicates that K3YbSi2O7 remains paramagnetic down to 2 K, showing no apparent influence of the phase transformation on its magnetic properties. Analysis of the magnetization data revealed the positions of the three lowest crystal field levels of the Yb3+ cations, as well as the corresponding projections of their angular momentum on the direction of the magnetic field.
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Romanenko, A. I., G. E. Chebanova, Tingting Chen, Wenbin Su et Hongchao Wang. « Review of the thermoelectric properties of layered oxides and chalcogenides ». Journal of Physics D : Applied Physics 55, no 14 (3 décembre 2021) : 143001. http://dx.doi.org/10.1088/1361-6463/ac3ce6.
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Abstract The current state of investigation on thermoelectric properties of layered chalcogenides and oxides is considered. The relationship between the quasi-two-dimensionality of electronic transport properties and thermoelectric properties is confirmed. A decrease in the dimension of electron transport from three-dimensional to quasi-two-dimensional in materials with a layered structure increases the thermopower with a slight change in electrical conductivity. The bismuth tellurides, bismuth selenides and its alloys are currently one of the outstanding state of the art bulk thermoelectric materials with layered structure. Layered transition metal dichalcogenides MX2 (M is a transition metal, X is a chalcogen) are efficient thermoelectric materials at higher temperatures (500–800 K). In these materials, an increase in thermoelectric properties associated with the two-dimensionalization of electron transport is also observed. Layered monochalcogenides MX (M = Sn, Pb, Ge; X = S, Se, Te) are also a promising class of thermoelectric materials. In SnSe single crystals, Z T ∼ 2.6 is obtained at 923 K due to the very low thermal conductivity along the b axis (0.23 W (m K)−1 at 973 K). Layered chalcogenides CuCrX2 (X = S, Se, Te) containing magnetic Cr atoms are effective thermoelectrics at higher temperatures (up to 800 K) due to the presence of phonon glass–electron crystal state led to a significant decrease in thermal conductivity at high temperatures. Magnetic atoms in CuCrX2 compounds lead to the presence of magnetic phase transitions affecting their thermoelectric properties. Interest in oxide-based thermoelectric materials has significantly increased due to their stability in air and higher temperatures for maximum efficiency. The most promising thermoelectric oxide materials Ca3Co4O9, Na x CoO2, Bi2Ca2Co2O x , and CaCo2O4 have a layered structure and contain magnetic Co atoms leading to magnetic ordering and influence on thermoelectric properties. The presence of phase transitions affects the thermoelectric parameters of thermoelectrics and the thermoelectric figure of merit ZT.
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Chiromawa, Idris Muhammad, Amiruddin Shaari, Razif Razali, Summanuwa Timothy Ahams et Mikailu Abdullahi. « Ab initio Investigation of the Structure and Electronic Properties of Normal Spinel Fe2SiO4 ». Malaysian Journal of Fundamental and Applied Sciences 17, no 2 (29 avril 2021) : 195–201. http://dx.doi.org/10.11113/mjfas.v17n2.2018.
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Transition metal spinel oxides have recently been predicted to create efficient transparent conducting oxides for optoelectronic devices. These compounds can be easily tuned by doping or defect to adapt their electronic or magnetic properties. However, their cation distribution is very complex and band structures are still subject to controversy. We propose a complete density functional theory investigation of fayalite (Fe2SiO4) spinel, using Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA) in order to explain the electronic and structural properties of this material. A detailed study of their crystal structure and electronic structure is given and compared with experimental data. The lattice parameters calculated are in agreement with the lattice obtained experimentally. The band structure of Fe2SiO4 spinel without Coulomb parameter U shows that the bands close to Fermi energy appear to be a band metal, with four iron d-bands crossing the Fermi level, in spite of the fact that from the experiment it is found to be an insulator.
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Han, J. P., et Y. Q. Guo. « Structure stability and magnetic properties of RIn3−xTx (R = Gd, Pr,T = Co, Fe, Mn) ». Powder Diffraction 32, no 4 (décembre 2017) : 249–54. http://dx.doi.org/10.1017/s0885715617001142.
Texte intégralRésumé :
The syntheses and crystal structures and magnetic properties of novel RIn3−xTx (R = Gd，Pr；T = Fe，Co，Mn；x = 0–0.3) intermetallic compounds in rare earth-In-3d transition metal ternary system have been systematically investigated. It reveals that RIn3−xTx crystallizes in cubic AuCu3 type structure with a space group of Pm$\bar 3$m and Z = 1. The 1a and 3c crystal positions are occupied by R and In atoms, respectively. The 3d transition metals substitute partly for In and prefer to occupy the 3c site. The lattice parameters and unit cell volumes decrease with increasing the content of 3d transition metal in RIn3−xTx intermetallic compounds. The magnetic properties of RIn3−xTx are sensitive to T content. With increasing T content, GdIn3−xTx alloys show the paramagnetic, mixture of ferromagnetic and paramagnetic and ferromagnetic behavior. T doping into RIn3 induces the presence of ferromagnetic phase in GdIn3−xTx, which is totally different from those of the pure binary RIn3.
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Zhang, Qin, Heng Chang Qian, Juan Pei et Suo Jia Yuan. « Competing Effects of Band Filling and Steric Factors on Magnetic and Transport Properties of Double Perovskite ». Advanced Materials Research 490-495 (mars 2012) : 325–28. http://dx.doi.org/10.4028/www.scientific.net/amr.490-495.325.
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Ordered double perovskite oxides (Sr2-3xLa2xBax)FeMoO6 (0≤x≤0.3) have been investigated in this work. X-ray powder diffraction reveals that the crystal structure of the compounds changes from a tetragonal I4/m lattice to a cubic Fm m lattice around x=0.2. Due to the electron doping, the lattice constants increase with x. Owing to the competing contribution of electron doping and steric effect, Curie temperature of the compounds is almost unchanged. The resistivity of the parent compound shows a semiconducting behavior below room temperature, but those of the doped samples exhibit a metal-semiconductor transition. A correlation between the resistivity and metal-semiconducting transition temperature (TM-S) is observed. The resistivity and TM-S of the compounds decrease with x for x 0.2 and increase for x≥0.2.
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Baker, Steve, Mervyn Roy, Chris Binns et Martin Lees. « Controlling Crystal Structure in Embedded Magnetic Nanoparticles ». Acta Crystallographica Section A Foundations and Advances 70, a1 (5 août 2014) : C961. http://dx.doi.org/10.1107/s205327331409038x.
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"Magnetic nanoparticles and nanocomposite materials have attracted much interest due to their novel magnetic behaviour, and their potential use in a range of applications. One of the main reasons for their novel magnetism, appreciated for some time, is the high proportion of under-coordinated atoms at the surface of nanoparticles. In the case of magnetic transition metals this leads to a narrowing of the 3d bands that are responsible for magnetism in these materials, leading to size-dependent nanoparticle properties. The atomic structure adopted by nanoparticles is also a key factor in determining their magnetism. Unlike in bulk materials atomic structure in nanoparticles can be changed more readily by, for example, embedding them in suitable matrix materials. Here we describe how a high level of control over crystal structure in nanoparticles can be achieved, using EXAFS to ""fingerprint"" their crystal structure, and show how this in turn leads to a high degree of control over nanoparticle magnetism. We describe a flexible co-deposition process based around a gas aggregation source, which enables a high degree of control over structure in transition metal nanoparticles embedded in various matrices. EXAFS experiments and analysis used to probe atomic structure in embedded Fe and Co nanoparticles are described [1]. Examples presented include the system of Fe nanoparticles embedded in a CuAu alloy matrix where we show that is not only the ability to change the atomic structure of embedded nanoparticles that is important but the ability to fine-tune their structure once changed [2]. In this case, this enables the atomic magnetic Fe moment to be fine-tuned to a value higher than in the bulk Fe structure, in agreement with theory. In some systems alloying at the particle/interface can be significant. We describe how this is the case for Fe nanoparticles in Pd [3], and how such alloying could be useful in forming magnetic nanocomposites with superior properties."
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Moshkina E. M., Molokeev M. S., Eremin E. V. et Bezmaternykh L. N. « Influence of Ga-substitution to the structural and magnetic properties of (Mn,Fe)-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- bixbyite ». Physics of the Solid State 65, no 6 (2023) : 1009. http://dx.doi.org/10.21883/pss.2023.06.56116.57.
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To study the dependence of the properties of ternary oxides (Mn,Fe,Ga)2O3 with the bixbyite structure on the composition, the temperature dependences of the magnetization and ac magnetic susceptibility of two single-crystal samples of different compositions obtained using the flux method were analyzed. A detailed study of the structure was carried out using single-crystal X-ray diffraction analysis, and the changes in structural parameters depending on the composition were analyzed. The dc magnetization and ac magnetic susceptibility of Fe1.1Mn0.76Ga0.14O3 and Fe0.65Mn1.1Ga0.26O3 bixbyites have been studied. Despite the qualitatively similar behavior of the magnetic properties, significant differences were also found, despite a small difference in the Mn/Fe/Ga ratio in the samples under study. It is shown that both compounds experience two successive low-temperature magnetic phase transitions from the paramagnetic phase at T=20-32 K as the temperature is lowered. Calculations of the Mydosh parameter for the detected phase transitions showed different degrees of ordering in the compounds under study. Keywords: transition metal oxides, magnetic phase transitions, spin glass state, bixbyite.
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Latushka, S. I., D. V. Zheludkevich, E. V. Budemko, K. N. Nekludov, M. V. Silibin et D. V. Karpinsky. « Crystal Structure and Magnetic Properties of Bi1-yBa(Sr)Fe1-yTiyO3 Solid Solutions ». Journal of Material Science and Technology Research 10 (29 août 2023) : 82–85. http://dx.doi.org/10.31875/2410-4701.2023.10.08.
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Abstract: Usages of various chemical substitution schemes of the initial multiferroic BiFeO3 can significantly reduce known drawbacks specific for the functional oxides based of iron ions and thus foster a creation of novel magnetoelectric compounds perspective for various technological applications. In the present study the co-doped compounds of the system Bi1-y(Ba1- xSrx)yFe1-yTiyO3 (x = 0.0 – 1.0; y ≤ 0.4) synthesized using sol-gel technique were analyzed focusing on the crystal structure stability and the correlation between the structure and magnetic properties. The concentration driven evolution of the crystal structure as well as the unit cell parameters were investigated based on the X-ray diffraction data, the correlation between the crystal structure and the magnetic properties of the compounds has been studied by magnetometry techniques. The compounds Bi1-y(Ba1- xSrx)yFe1-yTiyO3 with x = 0; y = ≤ 0.2 are characterized by single-phase rhombohedral structure, and increase in the dopant concentration to y = 0.4 leads to the stabilization of the pseudocubic phase. An increase in the Sr content leads to the phase transition in the compounds to the single phase state with the cubic structure which is accompanied by an increase in the value of the remanent magnetization.
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Demazeau, Gérard, Samir F. Matar et Rainer Pöttgen. « Chemical Bonding in Metallic Rutile-type Oxides TO2 (T = Ru, Rh, Pd, Pt) ». Zeitschrift für Naturforschung B 62, no 7 (1 juillet 2007) : 949–54. http://dx.doi.org/10.1515/znb-2007-0712.
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Abstract Synthesis routes to rutile-type oxides with 4d and 5d transition elements are summarized. Trends in electronic structure have been established through an analysis in the framework of density functional theory presenting the band structure, the density of states and the properties of chemical bonding. The metal-oxygen bond is found to play the major role in bonding of the system in the valence band. Throughout the series 4d → 5d (RuO2, RhO2, PdO2 and PtO2) the crystal field analysis of the band structure shows a lowering of eg towards t2g manifolds and a broadening of the overall density of states. In the vicinity of the Fermi level the role of the antibonding metal-oxygen character is investigated in the context of instability towards possible magnetic polarization, especially for RuO2.
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Yi, Di, Jian Liu, Shang-Lin Hsu, Lipeng Zhang, Yongseong Choi, Jong-Woo Kim, Zuhuang Chen et al. « Atomic-scale control of magnetic anisotropy via novel spin–orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices ». Proceedings of the National Academy of Sciences 113, no 23 (19 mai 2016) : 6397–402. http://dx.doi.org/10.1073/pnas.1524689113.
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Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e., magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry. Extrinsic control over the MA is usually achieved by introducing shape anisotropy or exchange bias from another magnetically ordered material. Here we demonstrate a pathway to manipulate MA of 3d transition-metal oxides (TMOs) by digitally inserting nonmagnetic 5d TMOs with pronounced spin–orbit coupling (SOC). High-quality superlattices comprising ferromagnetic La2/3Sr1/3MnO3 (LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control of thickness at the atomic scale. Magnetic easy-axis reorientation is observed by controlling the dimensionality of SIO, mediated through the emergence of a novel spin–orbit state within the nominally paramagnetic SIO.
Chapitres de livres sur le sujet "Novel Crystal Structure - Transition Metal Oxides - Magnetic Properties"
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Cao, Gang, et Lance E. DeLong. « Current Control of Structural and Physical Properties in Spin-Orbit- Coupled Mott Insulators ». Dans Physics of Spin-Orbit-Coupled Oxides, 135–58. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780199602025.003.0005.
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Electrical current as a means to control structural and related physical properties has been recognized only recently. The application of small electrical currents in sensitive detector and control applications, and in information technologies, is often preferable to other external stimuli. However, until recently it has not been widely accepted that electrical current can readily couple to the lattice, orbital, and spin degrees of freedom. Mounting experimental evidence has indicated that a combination of strong spin-orbit interactions and a distorted crystal structure in magnetic Mott insulators may be sufficient for electrical current to control structural and related properties. Current control of quantum states in 4d- and 5d-transition metal oxides has therefore rapidly expanded as a key research topic. This chapter presents two model systems, Ca2RuO4 and Sr2IrO4, in which applied current effectively controls the lattice, and thus the physical properties.
Actes de conférences sur le sujet "Novel Crystal Structure - Transition Metal Oxides - Magnetic Properties"
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Curtin, Paul R., Steve Constantinides et Patricia Iglesias Victoria. « Fracture Toughness of Samarium Cobalt Magnets ». Dans ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-53435.
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Samarium Cobalt (SmCo) magnets have been the magnet of choice for a variety of industries for many years due to their favorable magnetic properties. Their high coercivity, combined with a low temperature coefficient, make them the ideal permanent magnet for demanding high temperature applications. One of the biggest concerns with rare earth magnets is their brittleness. Samarium Cobalt magnets in particular are prone to fracturing during machining and assembly. In manufacturing, great care must be taken to avoid chipping or fracturing these magnets due to their brittle nature. There are two main grades of Samarium Cobalt magnets, 1:5 and 2:17. These ratios define the nominal ratio of rare earth to transition metal content. In this paper, an investigation is performed on the fracture toughness of permanent magnets based on the Samarium Cobalt 2:17 composition. Various techniques are used to characterize the microstructure of the material, and quantify the material properties. Optical microscopy is used to characterize the grain structure of the material and quantify the porosity of the material after sintering. By comparing the average grain size and fracture toughness of several samples, grain size was shown to not affect fracture toughness in standard material. Latent cracks in defective material showed no preference to follow grain boundaries, oxides inclusions or voids. River marks in fracture surfaces are seen through scanning electron microscopy, confirming the transgranular cracking pattern seen by Li et al [1]This suggests that the toughness of the material is an inherent property of the main phase, not of grain boundaries or contaminants. Samarium Cobalt magnets exhibit both mechanical and magnetic anisotropy due to the alignment of their crystal structure in the manufacturing process. Using Palmqvist indentation crack techniques, the magnetic orientation of the grains was seen to greatly influence the direction of crack propagation from the tip of the indenter. Measurements of fracture toughness using this technique produce highly scattered data due to this anisotropic nature of the material. Specimens loaded with the indenter axis parallel to the direction of orientation show normal Palmqvist cracks, while specimens loaded perpendicular to the direction of magnetization exhibit crack propagation initiating from the faces of the indenter. To better quantify the material’s brittleness, fracture testing is performed on specially prepared samples to obtain an absolute measure of fracture toughness (K1c). Results show that SmCo is measurably weaker than other magnetic materials such as neodymium iron boron magnets[2]. Furthermore, neither relative concentration of Samarium nor source of raw material show notable effect on the fracture toughness of the material.