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1. Polarized X-Rays from Windy Accretion in Cygnus X-1

   https://doi.org/10.3847/2041-8213/acd33e  

   Poutanen, Juri ; Veledina, Alexandra ; Beloborodov, Andrei M. ( May 2023 , The Astrophysical Journal Letters)

   Recent X-ray polarimetric data on the prototypical black hole X-ray binary Cyg X-1 from the Imaging X-ray Polarimetry Explorer present tight constraints on accretion geometry in the hard spectral state. Contrary to general expectations of a low, ≲1% polarization degree (PD), the observed average PD was found to be a factor of 4 higher. Aligned with the jet position angle on the sky, the observed polarization favors geometry of the X-ray emission region stretched normally to the jet in the accretion disk plane. The high PD is, however, difficult to reconcile with the low orbital inclination of the binaryi≈ 30°. We suggest that this puzzle can be explained if the emitting plasma is outflowing with a mildly relativistic velocity ≳0.4c. Our radiative transfer simulations show that Comptonization in the outflowing medium elongated in the plane of the disk and radiates X-rays with the degree and direction of polarization consistent with observations ati≈ 30°.

    

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2. Magnetic moments and spin structure in single-phase B20 Co 1+x Si 1−x (x = 0.043)

   https://doi.org/10.1063/5.0090545  

   Wang, Haohan ; Balasubramanian, Balamurugan ; Liu, Yaohua ; Streubel, Robert ; Pahari, Rabindra ; Ekanayaka, Thilini Kumari ; Mishra, Esha ; Klewe, Christoph ; Shafer, Padraic ; Dhall, Rohan ; et al ( May 2022 , Journal of Applied Physics)

   Neutron powder diffraction (NPD) and x-ray magnetic circular dichroism (XMCD) spectroscopy are employed to investigate the magnetism and spin structure in single-phase B20 Co_1.043Si_0.957. The magnetic contributions to the NPD data measured in zero fields are consistent with the helical order among the allowed spin structures derived from group theory. The magnitude of the magnetic moment is (0.3 ± 0.1) μ_B/Co according to NPD, while the surface magnetization probed by XMCD at 3 kOe is (0.18–0.31) μ_B/Co. Both values are substantially larger than the bulk magnetization of 0.11 μ_B/Co determined from magnetometry at 70 kOe and 2 K. These experimental data indicate the formation of a helical spin phase and the associated conical states in high magnetic fields.

    

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3. Superconductivity and Pronounced Electron‐Phonon Coupling in Rock‐Salt Al 1−x O 1−x and Ti 1−x O 1−x

   https://doi.org/10.1002/aelm.202400141  

   Žguns, Pjotrs ; Gedik, Nuh ; Yildiz, Bilge ; Li, Ju ( May 2024 , Advanced Electronic Materials)

   The highest ambient‐pressure Tc among binary compounds is 40 K (MgB2). Higher Tc is achieved in high‐pressure hydrides or multielement cuprates. Alternatively, are explored superconducting properties of binary, metastable sub‐oxides, that may emerge under extremely low oxygen partial pressure. The emphasis is on the rock‐salt structure, which is known to promote superconductivity, and exploring AlO, ScO, TiO, and NbO. Dynamic lattice stability is achieved by introducing metal and oxygen vacancies in the fashion of Nb_1−xO_1−x‐type structure (x = ¼). The electron‐phonon (e‐ph) coupling is remarkably large in Al_1−xO_1−xand Ti_1−xO_1−x(λ ≈ 2 at x = ¼), with Tc ≈ 35 K according to the Allen–Dynes equation. Significantly, the coupling strength is comparable to that in high‐pressure hydrides, yet, in contrast to hydrides and MgB2, the coupling is largely driven by low frequency phonons. Sc_1−xO_1−xand Nb_1−xO_1−xshow significantly smaller λ and Tc. Further, hydrogen intercalation to boost λ and Tc is investigated. Only Ti_1−x(O_1−xHx) and Nb_1−x(O_1−xHx) are dynamically stable upon intercalation, where H, respectively, decreases and increases Tc. The effect of H doping on electronic structure and Tc is discussed. Altogether, the study suggests that metal sub‐oxides are promising compounds to achieve strong e‐ph coupling at ambient pressure.

    

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4. High Curie temperature ferromagnetic structures of (Sb2Te3)1−x(MnSb2Te4)x with x = 0.7–0.8

   https://doi.org/10.1038/s41598-023-34585-y  

   Levy, Ido ; Forrester, Candice ; Ding, Xiaxin ; Testelin, Christophe ; Krusin-Elbaum, Lia ; Tamargo, Maria C. ( December 2023 , Scientific Reports)

   Abstract Magnetic topological materials are promising for realizing novel quantum physical phenomena. Among these, bulk Mn-rich MnSb 2 Te 4 is ferromagnetic due to Mn Sb antisites and has relatively high Curie temperatures (T C ), which is attractive for technological applications. We have previously reported the growth of materials with the formula (Sb 2 Te 3 ) 1−x (MnSb 2 Te 4 ) x , where x varies between 0 and 1. Here we report on their magnetic and transport properties. We show that the samples are divided into three groups based on the value of x (or the percent septuple layers within the crystals) and their corresponding T C values. Samples that contain x < 0.7 or x > 0.9 have a single T C value of 15–20 K and 20–30 K, respectively, while samples with 0.7 < x < 0.8 exhibit two T C values, one (T C1 ) at ~ 25 K and the second (T C2 ) reaching values above 80 K, almost twice as high as any reported value to date for these types of materials. Structural analysis shows that samples with 0.7 < x < 0.8 have large regions of only SLs, while other regions have isolated QLs embedded within the SL lattice. We propose that the SL regions give rise to a T C1 of ~ 20 to 30 K, and regions with isolated QLs are responsible for the higher T C2 values. Our results have important implications for the design of magnetic topological materials having enhanced properties. 

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5. Layered Oxides SrLaFe 1‐x Co x O 4‐δ (x=0–1) as Bifunctional Electrocatalysts for Water‐Splitting

   https://doi.org/10.1002/cctc.202100867  

   Alom, Md. Sofiul ; Ramezanipour, Farshid ( July 2021 , ChemCatChem)

   Multifunctional materials that are capable of facilitating multiple electrocatalytic processes are highly desirable. This work reports the observation of bifunctional electrocatalytic properties for water‐splitting in layered oxides, featuring 2‐dimensional layers of octahedrally coordinated transition metals separated by alkaline‐earth or rare‐earth metals. Remarkably, these materials are able to catalyze both half‐reactions of water‐splitting,i. e., oxygen‐evolution reaction (OER) and hydrogen‐evolution reaction (HER). Electrical charge‐transport studies of SrLaFe_1‐xCo_xO_4‐δin a wide range of temperatures, 25 to 800 °C, indicate semiconducting behavior for all three compounds, where there is a systematic increase in electrical conductivity as a function of temperature. The end member of the series, SrLaCoO_4‐δ, exhibits the highest electrical charge transport and best electrocatalytic activity toward both OER and HER. This catalyst also features the highest degree of polyhedral distortion as well as the presence of oxygen‐vacancies. In addition, the transition metals in this material have a favorable electronic configuration for enhanced electrocatalytic activity.

    

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