Structural properties of amorphous metal carbides: Theory and experiment

Kádas, Krisztina; Andersson, Matilda; Holmström, Erik; Wende, Heiko; Karis, Olof; Trabesinger, Sigita; Butorin, Sergei M.; Nikitenko, S. G.; Kvashnina, Kristina O.; Jansson, Ulf; Eriksson, Olle

doi:10.1016/j.actamat.2012.04.044

Cited by 20 publications

(29 citation statements)

References 54 publications

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“…This method is based on the single-random-valley approximation in vibration-transit (VT) theory [25,26]. The SQ method was demonstrated to provide reliable atomic coordinates of amorphous materials [24]. In the initial structures, 200 atoms were both spatially and chemically randomly distributed in a cubic unit cell with periodic boundary conditions and a density of = 7.87 g/cm 3 for Gd 0.24 Fe 0.76 , = 7.88 g/cm 3 for Gd 0.50 Fe 0.50 , and = 7.89 g/cm 3 for Gd 0.76 Fe 0.24 .…”

Section: A Details Of the Simulation Of Structural Propertiesmentioning

confidence: 99%

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All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics

et al. 2015

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In recent years there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e., first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshinskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbor exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.

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Section: A Details Of the Simulation Of Structural Propertiesmentioning

confidence: 99%

“…[24]. This method is based on the single-random-valley approximation in vibration-transit (VT) theory [25,26].…”

Section: A Details Of the Simulation Of Structural Propertiesmentioning

confidence: 99%

All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics

et al. 2015

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“…Disagreements between theory and experiment have been attributed to the fact that SQ is effectively a quench with an infinitely fast cooling rate [141]. However, this agreement may be a result of insufficient analytical rigour.…”

Section: Stochastic Quenching (Sq)mentioning

confidence: 97%

Computer simulations of glasses: the potential energy landscape

Raza

Alling

Abrikosov

2015

J. Phys.: Condens. Matter

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Abstract. We review the current state of research on glasses, discussing the theoretical background and computational models employed to describe them. This article focuses on the use of the potential energy landscape (PEL) paradigm to account for the phenomenology of glassy systems, and the way in which it can be applied in simulations and the interpretation of their results. This article provides a broad overview of the rich phenomenology of glasses, followed by a summary of the theoretical frameworks developed to describe this phenomonology. We discuss the background of the PEL in detail, the onerous task of how to generate computer models of glasses, various methods of analysing numerical simulations, and the literature on the most commonly used model systems. Finally, we tackle the problem of how to distinguish a good glass former from a good crystal former from an analysis of the PEL. In summarising the state of the potential energy landscape picture, we develop the foundations for new theoretical methods that allow the ab initio prediction of the glass-forming ability of new materials by analysis of the PEL.

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“…Amorphous phases can usually form at higher Si contents and at least X-ray amorphous films have been observed in several different Me-Si-C systems [15,21,38,39]. The amount of Si required to form a completely amorphous system is dependent on the metal.…”

Section: Me-si-cmentioning

confidence: 99%

Transition metal carbide nanocomposite and amorphous thin films

Tengstrand¹

2014

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The cover image shows a high resolution transmission electron microscopy image of a nanocomposite structure consisting of crystalline titanium carbide grains in an amorphous matrix of silicon and carbon. On the backside part of a selected area electron diffraction pattern from the same film is also seen.© Olof Tengstrand 2014 ISBN: 978-91-7519-398-4 ISSN: 0345-7524 Printed by LiU-Tryck Linköping, Sweden, 2014 i AbstractThis thesis explores thin films of binary and ternary transition metal carbides, in the Nb-C, Ti-Si-C, Nb-Si-C, Zr-Si-C, and Nb-Ge-C systems. The electrical and mechanical properties of these systems are affected by their structure and here both nanocomposite and amorphous thin films are thus investigated. By appropriate choice of transition metal and composition the films can be designed to be multifunctional with a combination of properties, such as low electric resistivity, low contact resistance and high mechanical strength. Electrical contacts are one example of application that has been of special interest in this thesis. Since some industrially important substrates used in electrical contacts soften at higher temperature, all films were deposited with dc magnetron sputtering at a low substrate temperature (200-350 °C).I show that the electrical resistivity and mechanical properties of composites consisting of nanocrystalline NbC grains (nc-NbC) in a matrix of amorphous C (a-C) depend strongly on the amount of amorphous C. The best combination of hardness (23 GPa) and electrical resistivity (260 µΩ*cm) are found in films with ~15 at.% a-C phase. This is a higher hardness and lower resistivity than measured for the more well studied Ti-C system if deposited under similar conditions. The better results can be explained by a thinner matrix of amorphous C phase in the case of NbC. The nc-NbC/a-C is therefore interesting as a material in electrical contacts.Si can be added to further control the structure and thereby the properties of binary Me-C systems. There are however, different opinions in the literature of whether Si is incorporated on the Ti or C site in the cubic NaCl (B1) structure of TiC. In order to understand how Si is incorporated in a Me-Si-C material I use a model system of epitaxial TiC x (x ~0.7). In this model system a few atomic percent of Si can be incorporated in the cubic TiC structure. The experimental results together with theoretical stability calculations suggest that the Si is positioned at the C sites forming Ti(Si,C) x . The calculation further shows a strong tendency for Si segregation, which is seen at higher Si contents in the experiments, where Si starts segregate out from the TiC x to the grain boundaries causing a loss of epitaxy.If Si is added to an Nb-C nanocomposite, it hinders the grain growth and thus a reduced size of the NbC grains is observed. The Si segregates to the amorphous matrix forming a-SiC. At the same time the resistivity increases and the hardness is reduced. With even higher amounts of Si (>25 at.%) into the Nb-Si-C material, grain gr...

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Structural properties of amorphous metal carbides: Theory and experiment

Cited by 20 publications

References 54 publications

All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics

All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics

Computer simulations of glasses: the potential energy landscape

Transition metal carbide nanocomposite and amorphous thin films

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