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Daniel Nerz

Bio: Daniel Nerz is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Thin film & Pulsed laser deposition. The author has an hindex of 1, co-authored 2 publications receiving 2 citations.

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TL;DR: In this paper, an analytical transmission electron microscopy (TEM) was applied to analyze the microstructure and secondary phases of Co-doped BaFe(2$As$_2$ ) with different growth rates.
Abstract: Thin films of Co-doped BaFe$_2$As$_2$ of similar thickness (~40 nm) were grown with different growth rates (0.4 A s$^{-1}$ and 0.9 A s$^{-1}$) by pulsed laser deposition on CaF$_2$(001) substrates. Analytical transmission electron microscopy (TEM) was applied to analyze the microstructure and secondary phases. The formation of BaF$_2$ and a high concentration of planar defects (mainly stacking faults) are observed for the sample grown at a low rate. A higher growth rate results in high-quality epitaxial films with only few antiphase boundaries. A higher $T_\text{c}$ was measured for the sample grown at a low growth rate, which is attributed to the difference in strain state induced by the high concentration of defects. Large crystalline Fe precipitates are observed in both samples. Chemical analysis shows a pronounced O and slight F content at the planar defects which highlights the role of O in defect formation. Electron-beam-induced irradiation damage during TEM measurements is observed and discussed.

4 citations


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TL;DR: In this article, the authors used aberration-corrected scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) to observe a universal behavior in the hole concentration and magnetic moment across different families.
Abstract: Iron-based superconductors (FBS) comprise several families of compounds having the same atomic building blocks for superconductivity, but large discrepancies among their physical properties. A longstanding goal in the field has been to decipher the key underlying factors controlling TC and the various doping mechanisms. In FBS materials this is complicated immensely by the different crystal and magnetic structures exhibited by the different families. In this paper, using aberration-corrected scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS), we observe a universal behavior in the hole concentration and magnetic moment across different families. All the parent materials have the same total number of electrons in the Fe 3d bands; however, the local Fe magnetic moment varies due to different orbital occupancy. Although the common understanding has been that both long-range and local magnetic moments decrease with doping, we find that, near the onset of superconductivity, the local magnetic moment increases and shows a dome-like maximum near optimal doping, where no ordered magnetic moment is present. In addition, we address a longstanding debate concerning how Co substitutions induces superconductivity in the 122 arsenide family, showing that the 3d band filling increases a function of doping. These new microscopic insights into the properties of FBS demonstrate the importance of spin fluctuations for the superconducting state, reveal changes in orbital occupancy among different families of FBS, and confirm charge doping as one of the mechanisms responsible for superconductivity in 122 arsenides.

17 citations

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TL;DR: In this paper, the presence of oxygen on the surfaces of flux grown BaFe2As2 single crystals which were kept in air ambience for several months was found by Energy Dispersive X-ray Analysis (EDAX).
Abstract: Presence of Oxygen (O2) has been found by Energy Dispersive X-ray Analysis (EDAX) on the surfaces of flux grown BaFe2As2 single crystals which were kept in air ambience for several months. Transport studies show that the O2 adsorbed crystals are more resistive and do not display any sharp slope change near 140 K which is the well known Spin Density Wave (SDW) transition temperature (TSDW) accompanying structural transition for as grown BaFe2As2. An anomalous slope change in resistivity is observed around 18 K at 0 and 5T. Magnetoresistance (MR) is noticed to increase as a function of applied field (H) quite differently than that for as grown crystals below TSDW which may be attributed to aging effec

5 citations

Journal ArticleDOI
TL;DR: The applications, advantages, and challenges of usingAI in material discovery are discussed and the future perspective of using AI in clean energy is studied to pave the way for a better understanding of the future of AI applications in clean energies.
Abstract: Artificial intelligence (AI)‐assisted materials design and discovery methods can come to the aid of global concerns for introducing new efficient materials in different applications. Also, a sustainable clean future requires a transition to a low‐carbon economy that is material‐intensive. AI‐assisted methods advent as inexpensive and accelerated methods in the design of new materials for clean energies. Herein, the emerging research area of AI‐assisted material discovery with a focus on developing clean energies is discussed. The applications, advantages, and challenges of using AI in material discovery are discussed and the future perspective of using AI in clean energy is studied. This perspective paves the way for a better understanding of the future of AI applications in clean energies.

3 citations

Journal ArticleDOI
TL;DR: In this paper , the authors successfully synthesized bulk Ba0.6Na0.4Fe2As2 and Sr0.5Na 0.5Fe 2As2 compounds by high-energy mechanical alloying (MA) technique.
Abstract: We successfully synthesized bulk Ba0.6Na0.4Fe2As2 and Sr0.5Na0.5Fe2As2 compounds by high-energy mechanical alloying (MA) technique. The MA process results in homogeneous amorphous phases of BaFe2As2 and SrFe2As2. It was found that the optimum time for high-energy milling in all cases is about 1.5–2 h, and the maximum amount of amorphous phase could be obtained when energy of 50–100 MJ/kg was absorbed by the powder. After a short-term heat treatment, we obtained nearly optimum sodium-doped Ba1−xNaxFe2As2 and Sr1−xNaxFe2As2 superconducting bulk samples. Therefore, MA is a potential scalable method to produce bulk superconducting material for industrial needs.