1,721,056 research outputs found
Evolution of magnetic properties in F-doped brownmillerite Ca 2 Fe 2 O 5
No full textBrownmillerite structure is derived from an ordered arrangement of oxygen vacancies within a perovskite structure, where alternating stacked layers of tetrahedral and octahedral units are formed with oxygen vacancy channels aligned in the tetrahedral layer. Naturally it becomes an important proposition to attempt anion engineering with such structures. Accordingly, we have synthesized oxyfluoride of brownmillerite Ca 2 Fe 2 O 5 by low temperature fluorination technique with poly(vinylidene fluoride) as a fluorinating agent. The global as well as local structural changes and the magnetic properties upon fluorination were investigated. Extended X-Ray Absorbtion Fine Structure Spectroscopy (EXAFS) confirmed substitution of oxygen by fluorine at the tetrahedral sites, thereby changing the oxidation state of Fe which in turn tunes the magnetic properties converting the parent G-type antiferromagnet structure to a spin glass-like one at low temperature
Identifying the nature of dielectric anomalies in SrFeO3−
No full textEarlier comprehensive study of SrFeO3−δ series of compounds showed interplay between the oxygen vacancy and the magnetic and transport properties of the system. We have synthesized a powder sample of SrFeO3−δ series with oxygen vacancy in the range . X-ray powder diffraction confirms the tetragonal crystal structure of the compound while the magnetic data indicates the presence of response from both orthorhombic (Sr4Fe4O11) and tetragonal (Sr8Fe8O23) phases which is common for the series with intermediate compositions. The temperature dependent dielectric measurements have been carried out in the 10 kHz–1 MHz frequency range. The dielectric constant and loss are found to be nearly temperature independent for around room temperature. This temperature independent response could possibly be referred to as ‘flat loss’ corresponding to a low loss behavior, making the compound a potential candidate to capacitor industry. The anion stoichiometry has been further manipulated by introducing a more electronegative fluoride anion in the vacant oxygen sites where the structure changes to cubic one at room temperatur
Investigating the development of spurious magnetism in single crystalline BaTi 0.95 Fe 0.05 O 3- d with high d by local structural probes
No full textSignature of covalency and disorder on the dielectric and magnetic properties of Ba6Co6ClO16
No full textHexagonal barium cobalt oxychlorides are an interesting class of materials showing complex interplay between Co-O covalency driven local structural distortions which give rise to strong anomalies in their dielectric and magnetic responses as a function of temperature. The unavoidable presence of oxygen vacancy induces further distortions and frequency dependent fluctuations. Similar instabilities are also found in the title compound Ba6Co6ClO16. These distortions simultaneously affect dielectric and magnetic structure of the compound which may point toward a new pathway to achieve multiferroicity
Formation of two-dimensional ordered nanodomains and curious properties of Sr<inf>3</inf>FeMoO<inf>7</inf>
No full textSr3FeMoO7 is a n = 2 Ruddlesden-Popper analogue of the famous double perovskite Sr2FeMoO6 (SFMO), where every two layers of transition metal BO6 (B = Fe, Mo) octahedral planes are interrupted along the c-direction by a SrO layer. Interestingly, these two-dimensional BO6 layers are found to form many highly ordered Fe-O-Mo flat nanodomains separated by antiphase boundaries (APBs) and the interaction between these disc-like ordered domains give rise to interesting magnetic, transport, and magnetotransport properties, such as large magnetoresistance as well as a strong electroresistance
Determinants and implications of fee changes in the hedge fund industry
Full text linkWe examine the determinants and consequences of changes in hedge fund fee structures. We show that fee changes are asymmetric with much greater incidence of fee increases compared to fee decreases. We find that managers of younger and smaller funds are more likely to increase fees after good performance. Investors view the fee increases following good performance as a signal of managerial ability only to be disappointed by their worse future performance. Taken together, these findings are consistent with opportunistic behavior of emerging fund managers in expropriating surplus from their investors. --
Re-examining the nature of ordering in CaMnO2 : The role of Mn-O covalency in the local structure
No full textCationic order versus La-O covalency in LaA (Ca,Ba) VMoO6 double perovskites
No full textWe have investigated the structural and physical properties of double perovskite (DP) LaAVMoO6 (A=Ca2+, Ba2+; abbreviated as LCVMO and LBVMO from now on) compounds, proposed to be possible half-metallic antiferromagnets (HMAFMs). Here we show that within LaAVMoO6 double perovskite structure, La-O covalency competes against B-site as well A-site cationic order and this competition critically influences their physical properties. Evidently, the presence of Ca2+ or Ba2+ at the A site along with La3+ would offer a tool to modify the A-site ordering and consequently influence the La-O covalency as well. Our experimental results reveal that LCVMO lies at the extreme end of this family and accommodates large scale phase separation in terms of La, V, and Ca, Mo-rich phases as a result of dominant La-O covalency. On the other hand, LBVMO is more correctly described as a layered A-site ordered and nearly complete B-site disordered double perovskite where cationic order dominates the La-O covalency. The general trend of our experimental findings is in agreement with the ab initio electronic structure calculations, carried out on realistic structures based on local coordination obtained from extended x-ray-absorption fine-structure study
Fluorinated hexagonal 4H SrMnO 3 : a locally disordered manganite
No full textThe structural, magnetic and dielectric properties of the hexagonal four-layered form of SrMnO 3 along with its fluorinated counterpart have been investigated. Among these, the fluorinated hexagonal four-layered compound is being reported for the first time. Although the bulk crystal structure does not change with fluorination, there are clear spectroscopic evidences of local chemical fluorination having disordered Mn-F rich phases in the fluorinated compound. Fluorination of bulk antiferromagnetic SrMnO 3 changes the magnetic properties considerably where a spin- or cluster-glass-like state appears below 42 K with a large exchange bias. In addition to that, the F-doped SrMnO 3 indicates development of polarization and the system exhibits ferroelectric nature which has been confirmed through the strain-electric field (S-E) hysteresis loop
Structural Rearrangement Followed by Entrapment of Subnanometer Building Blocks of Iron Oxyhydroxide in Aqueous Iron Chloride Solutions
No full textIron oxyhydroxide, a natural nanophase of iron found in the environment, plays a crucial role in regulating surface and groundwater composition. Recent research proposes that within the nonclassical prenucleation cluster growth model, subnanometer-sized clusters (olation clusters/Fe-13 delta-Keggin oxolation clusters) might act as the prenucleation clusters (PNCs) of ferrihydrite or iron oxyhydroxide solid phase. However, these clusters are difficult to characterize as they are only observable momentarily in low-pH, high-Fe concentration solutions before agglomerating into extended solids, keeping the controversy over the true nature of the PNCs alive. In this study, we introduce large quantities of zinc acetate salt (ZA) into iron chloride solutions at the olation-oxolation boundary (3.6 mM Fe3+ at pH similar to 2.6). Remarkably, this manipulation is found to alter the structural arrangement of these subnanometer clusters before blocking them in isolation for hours, even at pH 6, where extended iron oxyhydroxide phases typically precipitate. On the other hand, controlled addition of ZA allows partial unblocking, leading to anisotropic agglomeration into cylindrical rod-like structures. Experimental techniques such as synchrotron-based small-angle X-ray scattering, X-ray absorption spectroscopy, high-resolution transmission electron microscopy (TEM), and cryo-TEM, along with density functional theory (DFT) calculations, reveal the nature of the structural rearrangement and the crucial role of Zn2+ ions in cluster stabilization
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