Abstract
Experimental and theoretical investigations on itinerant ferromagnetic systems under pressure have shown that ferromagnetic quantum criticality is avoided either by a change of the ...transition order, becoming of the first order at a tricritical point, or by the appearance of modulated magnetic phases. In the first case, the application of a magnetic field reveals a wing-structure phase diagram as seen in itinerant ferromagnets such as ZrZn
2
and UGe
2
. In the second case, no tricritical wings have been observed so far. Here, we report on the discovery of wing-structure as well as the appearance of modulated magnetic phases in the temperature-pressure-magnetic field phase diagram of LaCrGe
3
. Our investigation of LaCrGe
3
reveals a double-wing structure indicating strong similarities with ZrZn
2
and UGe
2
. But, unlike these simpler systems, LaCrGe
3
also shows modulated magnetic phases similar to CeRuPO. This finding provides an example of an additional possibility for the phase diagram of metallic quantum ferromagnets.
Abstract
Unconventional superconductors have Cooper pairs with lower symmetries than in conventional superconductors. In most unconventional superconductors, the additional symmetry breaking occurs ...in relation to typical ingredients such as strongly correlated Fermi liquid phases, magnetic fluctuations, or strong spin-orbit coupling in noncentrosymmetric structures. In this article, we show that the time-reversal symmetry breaking in the superconductor LaNiGa
2
is enabled by its previously unknown topological electronic band structure, with Dirac lines and a Dirac loop at the Fermi level. Two symmetry related Dirac points even remain degenerate under spin-orbit coupling. These unique topological features enable an unconventional superconducting gap in which time-reversal symmetry can be broken in the absence of other typical ingredients. Our findings provide a route to identify a new type of unconventional superconductors based on nonsymmorphic symmetries and will enable future discoveries of topological crystalline superconductors.
Magnetic carbon nanotubes (CNTs)/alumina (Al
2
O
3
) nanocomposites were synthesized by the direct growth of CNTs on alumina by chemical vapor deposition (CVD) process. X-ray diffraction studies show ...that the crystalline structure of alumina nanoparticles remains preserved during the CVD process. Electron microscopy studies reveal the uniform distribution of CNTs within the alumina matrix. CNTs of average diameter 20 nm are spread around alumina particles of size 120 nm. The proportion of CNTs in alumina composites is determined to be approximately 10% from the thermogravimetric analysis. CNT-reinforced alumina nanocomposites demonstrate a significant improvement of the magnetic properties as compared with pristine alumina powder. The diamagnetic property of alumina nanopowder is transformed into a strongly pronounced ferromagnetic response upon the incorporation of CNTs. The saturation magnetization increased by ~ 2500%, and a pronounced coercivity of 68 Oe was observed in the nanocomposites. It is suggested that the encapsulation of cobalt inside the CNTs constrains the magnetic moments to result in higher saturation magnetization. Hence, the CNTs/Al
2
O
3
system synthesized in this work can be employed to engineer novel ceramic composites with enhanced magnetic properties.
In recent times, transformer networks have achieved state-of-the-art performance in a wide range of natural language processing tasks. Here we present a workflow based on the fine-tuning of BERT ...models for different downstream tasks, which results in the automated extraction of structured information from unstructured natural language in scientific literature. Contrary to existing methods for the automated extraction of structured compound-property relations from similar sources, our workflow does not rely on the definition of intricate grammar rules. Hence, it can be adapted to a new task without requiring extensive implementation efforts and knowledge. We test our data-extraction workflow by automatically generating a database for Curie temperatures and one for band gaps. These are then compared with manually curated datasets and with those obtained with a state-of-the-art rule-based method. Furthermore, in order to showcase the practical utility of the automatically extracted data in a material-design workflow, we employ them to construct machine-learning models to predict Curie temperatures and band gaps. In general, we find that, although more noisy, automatically extracted datasets can grow fast in volume and that such volume partially compensates for the inaccuracy in downstream tasks.
The pressure dependence of the structural, magnetic, and superconducting transitions and of the superconducting upper critical field were studied in sulfur-substituted Fe(Se1−xSx). Resistance ...measurements were performed on single crystals with three substitution levels (x=0.043, 0.096, 0.12) under hydrostatic pressures up to 1.8 GPa and in magnetic fields up to 9 T and were compared to data on pure FeSe. Our results illustrate the effects of chemical and physical pressure on Fe(Se1−xSx). On increasing sulfur content, magnetic order in the low-pressure range is strongly suppressed to a small domelike region in the phase diagrams. However, Ts is much less suppressed by sulfur substitution, and Tc of Fe(Se1−xSx) exhibits similar nonmonotonic pressure dependence with a local maximum and a local minimum present in the low-pressure range for all x. The local maximum in Tc coincides with the emergence of the magnetic order above Tc. At this pressure the slope of the upper critical field decreases abruptly, which may indicate a Fermi-surface reconstruction. The minimum of Tc correlates with a broad maximum of the upper critical field slope normalized by Tc.
The pressure dependence of the upper critical field, H sub(c2,c), of single crystalline FeSe was studied using measurements of the interplane resistivity, rho sub(c), in magnetic fields parallel to ...tetragonal c axis. H sub(c2,c)(T) curves obtained under hydrostatic pressures up to 1.56 GPa, the range over which the superconducting transition temperature, T sub(c), of FeSe exhibits a nonmonotonic dependence with local maximum at p sub(1) approximate 0.8 GPa and local minimum at p sub(2) approximate 1.2 GPa. The slope of the upper critical field at T sub(c), (dH sub(c2,c)/dT ) sub(Tc), also exhibits a nonmonotonic pressure dependence with distinct changes at p sub(1) and p sub(2). For p < p sub(1) the slope can be described within a multiband orbital model. For both p sub(1) < p < p sub(2) and p > p sub(2) the slope is in good semiquantitative agreement with a single band, orbital Helfand-Werthamer theory with Fermi velocities determined from Shubnikov-de Haas measurements. This finding indicates that Fermi surface changes are responsible for the local minimum of T sub(c)(p) at p sub(2) approximate 1.2 GPa.
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