Browsing by Author "Ji, H"

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    Fe Site order and magnetic properties of Fe1/4NbS2
    (American Chemical Society (ACS), 2023-11-06) Lawrence, EA; Huai, XD; Kim, DW; Avdeev, M; Chen, Y; Skorupskii, G; Miura, A; Ferrenti, A; Waibel, M; Kawaguchi, S; Ng, N; Kaman, B; Cai, Z; Schoop, L; Kushwaha, S; Liu, F; Tran, TT; Ji, H
    Transition-metal dichalcogenides (TMDs) have long been attractive to researchers for their diverse properties and high degree of tunability. Most recently, interest in magnetically intercalated TMDs has resurged due to their potential applications in spintronic devices. While certain compositions featuring the absence of inversion symmetry such as Fe1/3NbS2 and Cr1/3NbS2 have garnered the most attention, the diverse compositional space afforded through the host matrix composition as well as intercalant identity and concentration is large and remains relatively underexplored. Here, we report the magnetic ground state of Fe1/4NbS2 that was determined from low-temperature neutron powder diffraction as an A-type antiferromagnet. Despite the presence of overall inversion symmetry, the pristine compound manifests spin polarization induced by the antiferromagnetic order at generic k points, based on density functional theory band-structure calculations. Furthermore, by combining synchrotron diffraction, pair distribution function, and magnetic susceptibility measurements, we find that the magnetic properties of Fe1/4NbS2 are sensitive to the Fe site order, which can be tuned via electrochemical lithiation and thermal history. © 2023 American Chemical Society.
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    Local electronic and magnetic properties of the doped topological insulators Bi2Se3:Ca and Bi2Te3 : Mn investigated using ion-implanted 8Li β-NMR
    (American Physical Society (APS), 2020-12-28) McFadden, RML; Chatzichristos, A; Cortie, DL; Fujimoto, D; San Hor, Y; Ji, H; Karner, VL; Kiefl, RF; Levy, CDP; Li, RH; McKenzie, I; Morris, GD; Pearson, MR; Stachura, M; Cava, RJ; MacFarlane, WA
    We report β-NMR measurements in Bi2Se3:Ca and Bi2Te3:Mn single crystals using Li+8 implanted to depths on the order of 100 nm. Above ∼200K, spin-lattice relaxation reveals diffusion of Li+8, with activation energies of ∼0.4eV (∼0.2eV) in Bi2Se3:Ca (Bi2Te3:Mn). At lower temperatures, the NMR properties are those of a heavily doped semiconductor in the metallic limit, with Korringa relaxation and a small, negative, temperature-dependent Knight shift in Bi2Se3:Ca. From this, we make a detailed comparison with the isostructural tetradymite Bi2Te2Se [McFadden, Phys. Rev. B 99, 125201 (2019)2469-995010.1103/PhysRevB.99.125201]. In the magnetic Bi2Te3:Mn, the effects of the dilute Mn moments predominate, but remarkably the Li+8 signal is not wiped out through the magnetic transition at 13 K, with a prominent critical peak in the spin-lattice relaxation that is suppressed in a high applied field. This detailed characterization of the Li+8 NMR response is an important step toward using depth-resolved β-NMR to study the low-energy properties of the chiral topological surface state in the Bi2Ch3 tetradymite topological insulator. ©2024 American Physical Society.