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1. Effect of electron- and hole-doping on properties of kagomé-lattice ferromagnet Fe 3 Sn 2

   https://doi.org/10.1088/1361-648X/acc91e  

   Adams, Milo ; Huang, Chen ; Shatruk, Michael ( April 2023 , Journal of Physics: Condensed Matter)

   We report a theoretical investigation of effects of Mn and Co substitution in the transition metal sites of the kagomé-lattice ferromagnet, Fe₃Sn₂. Herein, hole- and electron-doping effects of Fe₃Sn₂have been studied by density-functional theory calculations on the parent phase and on the substituted structural models of Fe_3−xM_xSn₂(M = Mn, Co;x= 0.5, 1.0). All optimized structures favor the ferromagnetic ground state. Analysis of the electronic density of states (DOS) and band structure plots reveals that the hole (electron) doping leads to a progressive decrease (increase) in the magnetic moment per Fe atom and per unit cell overall. The high DOS is retained nearby the Fermi level in the case of both Mn and Co substitutions. The electron doping with Co results in the loss of nodal band degeneracies, while in the case of hole doping with Mn emergent nodal band degeneracies and flatbands initially are suppressed in Fe_2.5Mn_0.5Sn₂but re-emerge in Fe₂MnSn₂. These results provide key insights into potential modifications of intriguing coupling between electronic and spin degrees of freedom observed in Fe₃Sn₂.

    

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2. Spin Transitions and Compressibility of ε‐Fe 7 N 3 and γ′‐Fe 4 N: Implications for Iron Alloys in Terrestrial Planet Cores

   https://doi.org/10.1029/2020JB020660  

   Lv, Mingda ; Liu, Jiachao ; Zhu, Feng ; Li, Jie ; Zhang, Dongzhou ; Xiao, Yuming ; Dorfman, Susannah M. ( November 2020 , Journal of Geophysical Research: Solid Earth)

   Iron nitrides are possible constituents of the cores of Earth and other terrestrial planets. Pressure‐induced magnetic changes in iron nitrides and effects on compressibility remain poorly understood. Here we report synchrotron X‐ray emission spectroscopy (XES) and X‐ray diffraction (XRD) results for ε‐Fe₇N₃and γ′‐Fe₄N up to 60 GPa at 300 K. The XES spectra reveal completion of high‐ to low‐spin transition in ε‐Fe₇N₃and γ′‐Fe₄N at 43 and 34 GPa, respectively. The completion of the spin transition induces stiffening in bulk modulus of ε‐Fe₇N₃by 22% at ~40 GPa, but has no resolvable effect on the compression behavior of γ′‐Fe₄N. Fitting pressure‐volume data to the Birch‐Murnaghan equation of state yieldsV₀ = 83.29 ± 0.03 (ų),K₀ = 232 ± 9 GPa,K₀′ = 4.1 ± 0.5 for nonmagnetic ε‐Fe₇N₃above the spin transition completion pressure, andV₀ = 54.82 ± 0.02 (ų),K₀ = 152 ± 2 GPa,K₀′ = 4.0 ± 0.1 for γ′‐Fe₄N over the studied pressure range. By reexamining evidence for spin transition and effects on compressibility of other candidate components of terrestrial planet cores, Fe₃S, Fe₃P, Fe₇C₃, and Fe₃C based on previous XES and XRD measurements, we located the completion of high‐ to low‐spin transition at ~67, 38, 50, and 30 GPa at 300 K, respectively. The completion of spin transitions of Fe₃S, Fe₃P, and Fe₃C induces elastic stiffening, whereas that of Fe₇C₃induces elastic softening. Changes in compressibility at completion of spin transitions in iron‐light element alloys may influence the properties of Earth's and planetary cores.

    

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3. Structure and Oxidation States of Giant Unit Cell Compound Dy 117+x Fe 57–y Sn 112–z

   https://doi.org/10.1002/zaac.201700321  

   Brown, Alexander T. ; Barron, Keaton G. ; Salazar, Bryan G. ; Kirby, Parker ; McCandless, Gregory T. ; Walker, Amy V. ; Chan, Julia Y. ( November 2017 , Zeitschrift für anorganische und allgemeine Chemie)

   Motivated by the complex structure and properties of giant unit cell intermetallic compounds, a new isostructural Fe analogue of the Dy₁₁₇Co₅₇Sn₁₁₂structure type was synthesized. Single crystals of Dy₁₂₂Fe₅₅Sn₁₀₁were grown at 1260 °C via a Dy–Fe eutectoid flux. The Fe analogue also adopts the space groupFm3mwith lattice parametersa= 29.914(9) Å,V= 26769(23) ų, andZ= 4. Dy₁₂₂Fe₅₅Sn₁₀₁has a large cell volume, structural complexity, and consists of seven Dy, eight Fe, and ten Sn unique crystallographic sites. There are fifteen fully occupied atomic positions, three unique pairs of alternating atomic positions with positional disorder, and seven partially occupied atomic sites. Within this complex unit cell, only approximately half the unique atomic positions are fully occupied with the remainder of the atoms either positionally or occupationally disordered. X‐ray photoelectron spectroscopy indicates that the compound contains Dy³⁺, Fe⁰, Fe²⁺, Sn⁰, and Sn⁴⁺.

    

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4. Spin Wave Excitation, Detection, and Utilization in the Organic‐Based Magnet, V(TCNE) x (TCNE = Tetracyanoethylene)

   https://doi.org/10.1002/adma.202002663  

   Liu, Haoliang ; Malissa, Hans ; Stolley, Ryan M. ; Singh, Jaspal ; Groesbeck, Matthew ; Popli, Henna ; Kavand, Marzieh ; Chong, Su Kong ; Deshpande, Vikram V. ; Miller, Joel S. ; et al ( August 2020 , Advanced Materials)

   Spin waves, quantized as magnons, have low energy loss and magnetic damping, which are critical for devices based on spin‐wave propagation needed for information processing devices. The organic‐based magnet [V(TCNE)_x; TCNE = tetracyanoethylene;x≈ 2] has shown an extremely low magnetic damping comparable to, for example, yttrium iron garnet (YIG). The excitation, detection, and utilization of coherent and non‐coherent spin waves on various modes in V(TCNE)_xis demonstrated and show that the angular momentum carried by microwave‐excited coherent spin waves in a V(TCNE)_xfilm can be transferred into an adjacent Pt layer via spin pumping and detected using the inverse spin Hall effect. The spin pumping efficiency can be tuned by choosing different excited spin wave modes in the V(TCNE)_xfilm. In addition, it is shown that non‐coherent spin waves in a V(TCNE)_xfilm, excited thermally via the spin Seebeck effect, can also be used as spin pumping source that generates an electrical signal in Pt with a sign change in accordance with the magnetization switching of the V(TCNE)_x. Combining coherent and non‐coherent spin wave detection, the spin pumping efficiency can be thermally controlled, and new insight is gained for the spintronic applications of spin wave modes in organic‐based magnets.

    

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5. Using Light for Better Programming of Ferroelectric Devices: Optoelectronic MoS 2 ‐Pb(Zr,Ti)O 3 Memories with Improved On–Off Ratios

   https://doi.org/10.1002/aelm.202001223  

   Lipatov, Alexey ; Vorobeva, Nataliia S. ; Li, Tao ; Gruverman, Alexei ; Sinitskii, Alexander ( April 2021 , Advanced Electronic Materials)

   Ferroelectric (FE) devices are conventionally switched by an application of an electric field. However, the recent discoveries of light–matter interactions in heterostructures based on 2D semiconductors and FE materials open new opportunities for using light as an additional tool for device programming. Recently, a purely optical switching of FE polarization in heterostructures comprising 2D MoS₂and FE oxide perovskites, such as BaTiO₃and Pb(Zr,Ti)O₃(PZT), was demonstrated. In this work, it is investigated whether this optical switching has a practical value and can be used to improve functional characteristics of MoS₂‐PZT FE field‐effect transistors for nonvolatile memory applications. It is demonstrated that the combined use of an electrical field and visible light improves the nonvolatile ON/OFF ratios in MoS₂‐PZT memories by several orders of magnitude compared to their purely electrical operation. The memories are read at zero gate voltage (V_G) in darkness, but their ON and OFF currents, which routinely varied for different devices by over 10⁵, are achieved by programming at the sameV_G = −6 V with (ON state) and without (OFF state) light illumination, demonstrating its crucial importance. The light can likely serve as an important tool for better programming of a large variety of other semiconductor‐FE devices.

    

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