We report temperature-dependent Raman scattering and X-ray diffraction studies of pyrochlore iridates, (Eu\(_{1-x}\)Bi\(_x\))\(_2\)Ir\(_2\)O\(_7\), for x=0, 0.02, 0.035, 0.05 and 0.1. The temperature ...variation in Raman experiments spans from 4 K to 300 K, covering the metal-insulator phase transition accompanied by paramagnetic to all-in/all-out (AIAO) spin ordering (T\(_N\)). These systems also show a Weyl semi-metal (WSM) phase at low temperatures (below ~50 K). We show that the Ir-O-Ir bond bending mode, A\(_{1g}\) (510 cm\(^{-1}\)), shows anomalous softening in the magnetically ordered AIAO state, arising primarily from the spin-phonon interaction due to the phonon-modulation of the Dzyaloshinskii-Moriya (DM) spin-exchange interaction. The two stretching modes, T\(_{2g}^1\) (307 cm\(^{-1}\)) and T\(_{2g}^2\) (382 cm\(^{-1}\)) harden significantly in the magnetic insulating phase. The T\(_{2g}\) phonons also show anomalous temperature dependence of their mode frequencies, hitherto unreported, due to strong electron-phonon coupling. The signatures of the WSM state are observed in phonon renormalization below 50 K due to strong electron-phonon interaction. Our experimental results establish strong magneto-elastic coupling below T\(_N\) and significant electron-phonon interactions in the metallic phase above T\(_N\) as well as in the low-temperature WSM state.
The need for a fundamental understanding of the flow in metallic glasses has motivated a variety of experimental investigations involving temperature and strain-rate sensitivity tests and assessing ...the dependence of flow on microstructure and heat treatment. In order to elucidate the deformation mechanism and to increase the ductility of BMGs, the local variations in structure and/or composition play an important role. Such kind of structural modification can be induced by annealing at temperatures slightly below the glass transition temperature
T
g. The present work deals with two well-known Zr-based BMGs: Zr
55Cu
30Al
10Ni
5 and Zr
55Cu
20Al
10Ni
10Ti
5. Both BMGs show increased ductility after annealing, but the microstructural modifications are different.
The influence of ball milling on the atomic structure and magnetic properties of the Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} metallic glass with a high thermal stability and excellent soft magnetic ...properties has been investigated. After 14 h of milling, the obtained powders were found to consist mainly of an amorphous phase and a small fraction of the (Co,Fe){sub 21}Ta{sub 2}B{sub 6} nanocrystals. The changes in the reduced pair correlation functions suggest noticeable changes in the atomic structure of the amorphous upon ball milling. Furthermore, it has been shown that milling is accompanied by introduction of compressive and dilatational sites in the glassy phase and increasing the fluctuation of the atomic-level hydrostatic stress without affecting the coordination number of the nearest neighbors. Ball milling has decreased the thermal stability and significantly affected the magnetic properties through increasing the saturation magnetization, Curie temperature of the amorphous phase and coercivity. - Highlights: • Ball milling affected the atomic structure of Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} metallic glass. • Mechanically-induced crystallization started after 4 h milling. • Milling increased the fluctuation of the atomic-level hydrostatic stress in glass. • Ball milling influenced the thermal stability and magnetic properties.
In situ high-temperature X-ray diffraction experiments using high-energy photons and ab initio molecular dynamics simulations are performed to probe the temperature-induced changes in the topological ...short-range order in magnetron sputtered Co
67
B
33
metallic glass thin films. Based on this correlative experimental and theoretical study, the presence of B-Co-B rigid second-order structures at room temperature and the temperature-induced decrease in the population of these strongly bonded building blocks are inferred. This notion is consistent with experimental reports delineating the temperature dependence of elastic limit.
A gasket is an important constituent of a diamond anvil cell (DAC) assembly, responsible for the sample chamber stability at extreme conditions for x-ray diffraction studies. In this work, we studied ...the performance of gaskets made of metallic glass Fe0.79Si0.07B0.14 in a number of high-pressure x-ray diffraction (XRD) experiments in DACs equipped with conventional and toroidal-shape diamond anvils. The experiments were conducted in either uniaxial or radial geometry with x-ray beams of micron to sub-micron size. We report that the Fe0.79Si0.07B0.14 metallic glass gaskets offered stable sample environment under compression exceeding one megabar in all XRD experiments described here, even in those involving inter- or small-molecule gases (e.g. Ne, H2) used as pressure transmitting media or in those with laser heating in a DAC. These emphasize the material's importance for a great number of delicate experiments conducted under extreme conditions. Our results indicate that the application of Fe0.79Si0.07B0.14 metallic glass gaskets in XRD experiments of both uniaxial and radial geometries substantially improves the signal-to-noise ratio in comparison to that with conventional gaskets made of Re, W, steel or other crystalline metals.
The atomistic mechanisms occurring during the processes of aging and rejuvenation in glassy materials involve very small structural rearrangements that are extremely difficult to capture ...experimentally. Here we use in-situ X-ray diffraction to investigate the structural rearrangements during annealing from 77 K up to the crystallization temperature in Cu44Zr44Al8Hf2Co2 bulk metallic glass rejuvenated by high pressure torsion performed at cryogenic temperatures and at room temperature. Using a measure of the configurational entropy calculated from the X-ray pair correlation function, the structural footprint of the deformation-induced rejuvenation in bulk metallic glass is revealed. With synchrotron radiation, temperature and time resolutions comparable to calorimetric experiments are possible. This opens hitherto unavailable experimental possibilities allowing to unambiguously correlate changes in atomic configuration and structure to calorimetrically observed signals and can attribute those to changes of the dynamic and vibrational relaxations ({\alpha}-, {\beta}- and {\gamma}-transition) in glassy materials. The results suggest that the structural footprint of the {\beta}-transition is related to entropic relaxation with characteristics of a first-order transition. Dynamic mechanical analysis data shows that in the range of the {\beta}-transition, non-reversible structural rearrangements are preferentially activated. The low-temperature {\gamma}-transition is mostly triggering reversible deformations and shows a change of slope in the entropic footprint suggesting second-order characteristics.
The plasticity of metallic glasses depends largely on the atomic-scale structure. However, the details of the atomic-scale structure, which are responsible for their properties, remain to be ...clarified. In this study, in-situ high-energy synchrotron X-ray diffraction and strain-rate jump compression tests at different cryogenic temperatures were carried out. We show that the activation volume of flow units linearly depends on temperature in the non-serrated flow regime. A plausible atomic deformation mechanism is proposed, considering that the activated flow units mediating the plastic flow originate from the medium-range order and transit to the short-range order with decreasing temperature.
IMPACT STATEMENT
An atomic deformation mechanism in metallic glasses is proposed. Activated flow units mediating the plastic flow originate from the medium-range order and transit to the short-range order with decreasing temperature.
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