Modeling of Early Stages of Formation of Poly-CO

2012 ◽  
Vol 1405 ◽  
Author(s):  
I. G. Batyrev ◽  
W. D. Mattson ◽  
B. M. Rice
Keyword(s):  
Random Network ◽  
Normal Modes ◽  
Hysteresis Loops ◽  
Dipole Approximation ◽  
Cubic Phase ◽  
Random Structure ◽  
Zero Temperature ◽  
Experimental Ir ◽  
Early Stages ◽  
Minor Distortion

ABSTRACTWe studied the early stages of polymerization of CO under pressure. We performed DFT simulations of 128 and 432 atom models. Structures of random networks found at zero temperature were used for equilibration at 100 K by employing first principles MD. We found that the polymerization begins at 7 - 8 GPa and slightly depends on the size of the model. It turned out that there are several metastable phases of the extended CO solid, corresponding to different compression pressures from 7 - 8 GPa to 15-18 GPa with different numbers of CO fragments, not connected to the random network. We also found that the transition to the phases is irreversible which results in hysteresis loops. Random network structures obtained, say, under 18 GPa could exist at 3 GPa, whereas compression to 3 GPa results in the delta phase of CO crystal, with intact CO fragments and minor distortion of the cubic phase. To analyze the random structure fragments we calculated normal modes and IR intensities using the dipole approximation. Contributions from the main motifs of the random network are identified and compared with experimental IR measurements.

scholarly journals Asymmetric Hysteresis Loops in Structured Ferromagnetic Nanoparticles with Hard/Soft Areas

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 800
Author(s):  
Joscha Detzmeier ◽  
Kevin Königer ◽  
Tomasz Blachowicz ◽  
Andrea Ehrmann
Keyword(s):  
Magnetization Reversal ◽  
Thermal Effects ◽  
Hysteresis Loops ◽  
Ferromagnetic Nanoparticles ◽  
Zero Temperature ◽  
Small Deviations ◽  
Micromagnetic Simulations ◽  
Random Anisotropy ◽  
Ferromagnetic Nanostructures ◽  
Biased Samples

Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero temperature with sufficiently large saturation fields should not lead to such asymmetries. Here we report on micromagnetic simulations at zero temperature, performed on sputtered nanoparticles with different structures. The small deviations of the systems due to random anisotropy orientations in the different grains can not only result in strong deviations of magnetization reversal processes and hysteresis loops, but also lead to distinctly asymmetric, horizontally shifted hysteresis loops in purely ferromagnetic nanoparticles.

scholarly journals The Impact of Cation Distribution on The Structural and Magnetic Properties of Nonstoichiometric Co0.5Ni0.5+xFe2-xO4 Nanoferrites

2021 ◽  
Author(s):  
Adel Maher Wahba ◽  
Bahaa Eldeen M. Moharam ◽  
Aya Fayez Mahmoud
Keyword(s):  
Magnetic Properties ◽  
Crystallite Size ◽  
Cation Distribution ◽  
Hysteresis Loops ◽  
Lattice Parameter ◽  
Cubic Phase ◽  
Ir Frequencies ◽  
Structural And Magnetic Properties ◽  
Xrd Patterns ◽  
The Impact

Abstract In this work, the impact of nonstoichiometric substitution of Fe3+ cations by Ni2+ ones on the structural and magnetic properties of Co0.5Ni0.5+xFe2-xO4 (0.0 ≤ x ≤ 0.4) nanoferrites synthesized by citric autocombustion method. The cubic phase purity for sintered samples were verified by XRD patterns and FTIR spectra. The crystallite size and microstrain were deduced using Williamson-Hall method. The estimated crystallite size ranges from 55 to 89 nm in agreement with TEM microimages. Hysteresis loops traced using VSM prevailed a regular reduction of saturation magnetization with Ni substitution. Relied on the experimental data of XRD, FTIR, and VSM, cation distribution has been suggested, according to which the nonstoichiometric substitution was compensated by the appearance of higher valance states of Fe, Ni, and Co cations. The suggested cation distribution successfully explained the recorded data of lattice parameter, crystallite size, IR frequencies, magnetization and coercivity.

The elastic and dielectric properties of crystals with polarizable atoms

1962 ◽  
Vol 268 (1332) ◽  
pp. 121-144 ◽  
Keyword(s):  
Dipole Moments ◽  
Equations Of Motion ◽  
Normal Modes ◽  
Dipole Approximation ◽  
Dielectric Constants ◽  
Electronic Charge ◽  
Quadrupole Moments ◽  
Caesium Chloride ◽  
Zinc Blende ◽  
Modes Of Vibration

The equations of motion, in the dipole approximation, for the normal modes of vibration of a crystal with polarizable ions, are expanded by the method of long waves and separation of the macroscopic electric field. The elastic and dielectric constants are then obtained in terms of the interactions between the ions and the electronic dipole moments. The formulae are simplified for diagonally cubic crystals and explicit expressions deduced for the elastic constants of crystals having the sodium chloride, caesium chloride, and zinc blende structures. The theory is then extended to include the quadrupole moments of the electronic charge distribution and the elastic and dielectric constants obtained.

scholarly journals Hysteresis in Two-Dimensional Liquid Crystal Models

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Slavko Buček ◽  
Samo Kralj ◽  
T. J. Sluckin
Keyword(s):  
External Field ◽  
Numerical Study ◽  
Mean Field ◽  
Hysteresis Loops ◽  
Two Dimensional ◽  
Zero Temperature ◽  
Coupling Constant ◽  
Field Approach ◽  
Random Anisotropy ◽  
Internal Coupling

We make a numerical study of hysteresis loop shapes within a generalized two-dimensional Random Anisotropy Nematic (RAN) model at zero temperature. The hysteresis loops appear on cycling a static external ordering field. Ordering in these systems is history dependent and involves interplay between the internal coupling constantJ, the anisotropy random fieldD, and the ordering external fieldH. Here the external field is represented by a traceless tensor, analogous to extension-type fields in continuum mechanics. The calculations use both a mean field approach and full lattice simulations. Our analysis suggests the existence of two qualitatively different solutions, which we denote assymmetricandsymmetry breaking. For the set of parameters explored, only the symmetric solutions are stable. Both approaches yield qualitatively similar hysteresis curves, which are manifested either by single or double loops. But the quantitative differences indicate that mean field estimates are only of limited predictive value.

scholarly journals On the structure of cortical micro-circuits inferred from small sample sizes

2017 ◽  
Author(s):  
Marina Vegué ◽  
Rodrigo Perin ◽  
Alex Roxin
Keyword(s):  
Network Topology ◽  
Random Network ◽  
Small Sample ◽  
Spatial Distance ◽  
Random Structure ◽  
Sample Sizes ◽  
Apparent Paradox ◽  
Degree Correlation ◽  
Special Cases ◽  
Small Sample Sizes

AbstractThe structure in cortical micro-circuits deviates from what would be expected in a purely random network, which has been seen as evidence of clustering. To address this issue we sought to reproduce the non-random features of cortical circuits by considering several distinct classes of network topology, including clustered networks, networks with distance-dependent connectivity and those with broad degree distributions. To our surprise we found that all these qualitatively distinct topologies could account equally well for all reported non-random features, despite being easily distinguishable from one another at the network level. This apparent paradox was a consequence of estimating network properties given only small sample sizes. In other words, networks which differ markedly in their global structure can look quite similar locally. This makes inferring network structure from small sample sizes, a necessity given the technical difficulty inherent in simultaneous intracellular recordings, problematic. We found that a network statistic called the sample degree correlation (SDC) overcomes this difficulty. The SDC depends only on parameters which can be reliably estimated given small sample sizes, and is an accurate fingerprint of every topological family. We applied the SDC criterion to data from rat visual and somatosensory cortex and discovered that the connectivity was not consistent with any of these main topological classes. However, we were able to fit the experimental data with a more general network class, of which all previous topologies were special cases. The resulting network topology could be interpreted as a combination of physical spatial dependence and non-spatial, hierarchical clustering.Significance StatementThe connectivity of cortical micro-circuits exhibits features which are inconsistent with a simple random network. Here we show that several classes of network models can account for this non-random structure despite qualitative differences in their global properties. This apparent paradox is a consequence of the small numbers of simultaneously recorded neurons in experiment: when inferred via small sample sizes many networks may be indistinguishable, despite being globally distinct. We develop a connectivity measure which successfully classifies networks even when estimated locally, with a few neurons at a time. We show that data from rat cortex is consistent with a network in which the likelihood of a connection between neurons depends on spatial distance and on non-spatial, asymmetric clustering.

X-ray absorption studies of high performance Low-k dielectric materials

2002 ◽  
Vol 745 ◽  
Author(s):  
T. Yoda ◽  
H. Miyajima ◽  
M. Shimada ◽  
R. Nakata ◽  
H. Hashimoto
Keyword(s):  
High Performance ◽  
Bond Angle ◽  
Random Network ◽  
Xanes Spectrum ◽  
Dielectric Materials ◽  
Structure Change ◽  
Random Structure ◽  
Ladder Structure ◽  
Absorption Studies ◽  
Low K

ABSTRACTThe XAFS measurement of the MSQ type low-k dielectrics (LKD™) was conducted to clarify the structure change with and without the EB cure. Furthermore, three different types of other MSQ films, the ladder structure, the random structure and the CVD film, have been investigated as references. We have determined Si-O-Si bond angle and Si-O(Si-C) bond length by fitting the Fourier transformed EXAFS spectra.The ladder structure and the random structure have Si-O-Si bond angle of 133 and 146, respectively.Si-O-Si bond angle of LKD™ film is among that of the ladder and the random structure, and the XANES spectrum of LKD™ film displays two broad features, corresponding to the mixture of both structures. In contrast, Si-O-Si angles of the EB cured LKD™ film and the CVD film resemble each other, and the XANES features of both films are almost identical with that of the random structure.We have confirmed that the EB cure process for LKD™ film makes drastic structure change from the mixture of ladder and random structure to the random network structure.

Facile Fabrication of Magnetic Nanocomposites of Ordered Mesoporous Carbon Decorated with Nickel Nanoparticles

2007 ◽  
Vol 7 (2) ◽  
pp. 504-509 ◽  
Author(s):  
Yulin Cao ◽  
Jieming Cao ◽  
Mingbo Zheng ◽  
Jinsong Liu ◽  
Guangbin Ji ◽  
...  
Keyword(s):  
Mesoporous Carbon ◽  
Nickel Nanoparticles ◽  
Hysteresis Loops ◽  
Ordered Mesoporous Carbon ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Ordered Mesoporous ◽  
Special Surface ◽  
Facile Fabrication

A magnetic nanocomposite of ordered mesoporous carbon (CMK-3) decorated with nickel nanoparticles was synthesized successfully by a simple chemistry method. Nickel nanoparticles were prepared and uniformly supported on ordered mesoporous carbon CMK-3 by reduction route with CMK-3 as a reducing agent at 673 K. The Ni/CMK-3 composite materials were characterized by powder X-ray diffraction, nitrogen sorption, and transmission electron microscopy. As-prepared nickel nanoparticles supported on CMK-3 were crystalline with a face-center-cubic phase and a size distribution ranging from 10 to 60 nm. The BET special surface area and pore volume of Ni/CMK-3 were as high as 797 m2 g−1 and 0.72 cm3 g−1, respectively. The formation mechanism of the nickel nanoparticles outside the surface of CMK-3 was preliminarily discussed. The hysteresis loops of the CMK-3 decorated with nickel nanoparticles were measured by vibrating sample magnetometer (VSM), and the results showed that the composite was ferromagnetism with the saturated magnetization of 15 emu/g, and the coercivity value of 214 Oe. Furthermore, the application of Ni/CMK-3 as magnetically separable adsorbent for vitamin B2 was primarily examined in this study.

scholarly journals Asymmetric Hysteresis Loops and Horizontal Loop Shifts in Purely Ferromagnetic Nanoparticles

2020 ◽  
Vol 4 (1) ◽  
pp. 13
Author(s):  
Joscha Detzmeier ◽  
Kevin Königer ◽  
Andrea Ehrmann
Keyword(s):  
Thermal Effects ◽  
Hysteresis Loops ◽  
Ferromagnetic Nanoparticles ◽  
Zero Temperature ◽  
Small Deviations ◽  
Micromagnetic Simulations ◽  
Random Anisotropy ◽  
Ferromagnetic Nanostructures ◽  
Different Shapes ◽  
Biased Samples

Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange-coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero temperature with sufficiently large saturation fields should not lead to such asymmetries. Here we report on micromagnetic simulations at zero temperature, performed on sputtered nanoparticles with different shapes. The small deviations of the systems due to random anisotropy orientations in the different grains can not only result in strong deviations of magnetization reversal processes and hysteresis loops, but also to distinctly asymmetric, horizontally shifted hysteresis loops in purely ferromagnetic nanoparticles.

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