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1. Tetrairon( ii ) extended metal atom chains as single-molecule magnets

   https://doi.org/10.1039/d1dt01007g  

   Nicolini, Alessio ; Affronte, Marco ; SantaLucia, Daniel J. ; Borsari, Marco ; Cahier, Benjamin ; Caleffi, Matteo ; Ranieri, Antonio ; Berry, John F. ; Cornia, Andrea ( June 2021 , Dalton Transactions)

   null (Ed.)

   Iron-based extended metal atom chains (EMACs) are potentially high-spin molecules with axial magnetic anisotropy and thus candidate single-molecule magnets (SMMs). We herein compare the tetrairon( ii ), halide-capped complexes [Fe 4 (tpda) 3 Cl 2 ] ( 1Cl ) and [Fe 4 (tpda) 3 Br 2 ] ( 1Br ), obtained by reacting iron( ii ) dihalides with [Fe 2 (Mes) 4 ] and N 2 , N 6 -di(pyridin-2-yl)pyridine-2,6-diamine (H 2 tpda) in toluene, under strictly anhydrous and anaerobic conditions (HMes = mesitylene). Detailed structural, electrochemical and Mössbauer data are presented along with direct-current (DC) and alternating-current (AC) magnetic characterizations. DC measurements revealed similar static magnetic properties for the two derivatives, with χ M T at room temperature above that for independent spin carriers, but much lower at low temperature. The electronic structure of the iron( ii ) ions in each derivative was explored by ab initio (CASSCF-NEVPT2-SO) calculations, which showed that the main magnetic axis of all metals is directed close to the axis of the chain. The outer metals, Fe1 and Fe4, have an easy-axis magnetic anisotropy ( D = −11 to −19 cm −1 , | E / D | = 0.05–0.18), while the internal metals, Fe2 and Fe3, possess weaker hard-axis anisotropy ( D = 8–10 cm −1 , | E / D | = 0.06–0.21). These single-ion parameters were held constant in the fitting of DC magnetic data, which revealed ferromagnetic Fe1–Fe2 and Fe3–Fe4 interactions and antiferromagnetic Fe2–Fe3 coupling. The competition between super-exchange interactions and the large, noncollinear anisotropies at metal sites results in a weakly magnetic non-Kramers doublet ground state. This explains the SMM behavior displayed by both derivatives in the AC susceptibility data, with slow magnetic relaxation in 1Br being observable even in zero static field. 

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2. Two-dimensional Dirac spin-gapless semiconductors with tunable perpendicular magnetic anisotropy and a robust quantum anomalous Hall effect

   https://doi.org/10.1039/d0mh00396d  

   Sun, Qilong ; Ma, Yandong ; Kioussis, Nicholas ( August 2020 , Materials Horizons)

   null (Ed.)

   A major recent breakthrough in materials science is the emergence of intrinsic magnetism in two-dimensional (2D) crystals, which opens the door to more cutting-edge fields in the 2D family and could eventually lead to novel data-storage and information devices with further miniaturization. Herein we propose an experimentally feasible 2D material, Fe 2 I 2 , which is an intrinsic room-temperature ferromagnet exhibiting perpendicular magnetic anisotropy (PMA). Using first-principles calculations, we demonstrate that single-layer (SL) Fe 2 I 2 is a spin-gapless semiconductor with a spin-polarized Dirac cone and linear energy dispersion in one spin channel, exhibiting promising dissipation-less transport properties with a Fermi velocity up to 6.39 × 10 5 m s −1 . Our results reveal that both strain and ferroelectric polarization switching could induce an out-of- to in-plane spin reorientation in the 2D Fe 2 I 2 layer, revealing its advantage in assembling spintronic devices. In addition, spin–orbit coupling (SOC) triggers a topologically nontrivial band gap of 301 meV with a nonzero Chern number (| C | = 2), giving rise to a robust quantum anomalous Hall (QAH) state. The 2D crystal also exhibits high carrier mobilites of 0.452 × 10 3 and 0.201 × 10 3 cm 2 V −1 s −1 for the electrons and holes, respectively. The combination of these unique properties renders the 2D Fe 2 I 2 ferromagnet a promising platform for high efficiency multi-functional spintronic applications. 

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3. High-harmonic generation in spin and charge current pumping at ferromagnetic or antiferromagnetic resonance in the presence of spin–orbit coupling

   https://doi.org/10.1088/2515-7639/aceaad  

   Varela-Manjarres, Jalil ; Nikolić, Branislav K. ( August 2023 , Journal of Physics: Materials)

   One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, for example, thez-axis) with frequencyω₀due to absorption of low-power microwaves of frequencyω₀under the resonance conditions and in the absence of any applied bias voltage. The two-decades-old ‘standard model’ of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that component$I^{S_z}$of spin current vector$(I^{S_x}(t),I^{S_y}(t),I^{S_z})\propto {\omega }_0$is time-independent while$I^{S_x}(t)$and$I^{S_y}(t)$oscillate harmonically in time with a single frequencyω₀whereas pumped charge current is zero$I\equiv 0$in the same adiabatic$\propto {\omega }_0$limit. Here we employ more general approaches than the ‘standard model’, namely the time-dependent nonequilibrium Green’s function (NEGF) and the Floquet NEGF, to predict unforeseen features of spin pumping: namely precessing localized magnetic moments within a ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose conduction electrons are exposed to spin–orbit coupling (SOC) of either intrinsic or proximity origin, will pump both spin$I^{S_{\alpha }}(t)$and chargeI(t) currents. All four of these functions harmonically oscillate in time at both even and odd integer multiples$N{\omega }_0$of the driving frequencyω₀. The cutoff order of such high harmonics increases with SOC strength, reaching$N_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq 11$in the one-dimensional FM or AFM models chosen for demonstration. A higher cutoff$N_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq 25$can be achieved in realistic two-dimensional (2D) FM models defined on a honeycomb lattice, and we provide a prescription of how to realize them using 2D magnets and their heterostructures.

    

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4. Anisotropic Phonon Response of Few‐Layer PdSe 2 under Uniaxial Strain

   https://doi.org/10.1002/adfm.202003215  

   Luo, Weijun ; Oyedele, Akinola D. ; Gu, Yiyi ; Li, Tianshu ; Wang, Xingzhi ; Haglund, Amanda V. ; Mandrus, David ; Puretzky, Alexander A. ; Xiao, Kai ; Liang, Liangbo ; et al ( July 2020 , Advanced Functional Materials)

   PdSe₂, an emerging 2D material with a novel anisotropic puckered pentagonal structure, has attracted growing interest due to its layer‐dependent electronic bandgap, high carrier mobility, and good air stability. Herein, a detailed Raman spectroscopic study of few‐layer PdSe₂(two to five layers) under the in‐plane uniaxial tensile strain up to 3.33% is performed. Two of the prominent PdSe₂Raman peaks are influenced differently depending on the direction of strain application. The mode redshifts more than the mode when the strain is applied along thea‐axis of the crystal, while the mode redshifts more than the mode when the strain is applied along theb‐axis. Such an anisotropic phonon response to strain indicates directionally dependent mechanical and thermal properties of PdSe₂and also allows the identification of the crystal axes. The results are further supported using first‐principles density‐functional theory. Interestingly, the near‐zero Poisson’s ratios for few‐layer PdSe₂are found, suggesting that the uniaxial tensile strain can easily be applied to few‐layer PdSe₂without significantly altering their dimensions at the perpendicular directions, which is a major contributing factor to the observed distinct phonon behavior. The findings pave the way for further development of 2D PdSe₂‐based flexible electronics.

    

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5. Spin structure and dynamics of the topological semimetal Co3Sn2-xInxS2

   https://doi.org/10.1038/s41535-022-00523-w  

   Neubauer, Kelly J. ; Ye, Feng ; Shi, Yue ; Malinowski, Paul ; Gao, Bin ; Taddei, Keith M. ; Bourges, Philippe ; Ivanov, Alexandre ; Chu, Jiun-Haw ; Dai, Pengcheng ( December 2022 , npj Quantum Materials)

   The anomalous Hall effect (AHE), typically observed in ferromagnetic (FM) metals with broken time-reversal symmetry, depends on electronic and magnetic properties. In Co₃Sn_2-xIn_xS₂, a giant AHE has been attributed to Berry curvature associated with the FM Weyl semimetal phase, yet recent studies report complicated magnetism. We use neutron scattering to determine the spin dynamics and structures as a function ofxand provide a microscopic understanding of the AHE and magnetism interplay. Spin gap and stiffness indicate a contribution from Weyl fermions consistent with the AHE. The magnetic structure evolves fromc-axis ferromagnetism at$$x = 0$$$x=0$to a canted antiferromagnetic (AFM) structure with reducedc-axis moment and in-plane AFM order at$$x = 0.12$$$x=0.12$and further reducedc-axis FM moment at$$x = 0.3$$$x=0.3$. Since noncollinear spins can induce non-zero Berry curvature in real space acting as a fictitious magnetic field, our results revealed another AHE contribution, establishing the impact of magnetism on transport.

    

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