Browsing by Author "Yu, YS"

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    Large easy-plane anisotropy induced spin reorientation in magnetoelectric materials (Co4−xMnx)Nb2O9
    (IOP Science, 2019-03-29) Deng, GC; Yu, YS; Cao, YM; Feng, ZJ; Ren, W; Cao, SX; Studer, AJ; Hester, JR; Kareri, Y; Ulrich, C; McIntyre, GJ
    Neutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co4−xMnx)Nb2O9 (x  =  0, 1, 2, 3, 3.5, 3.9, 3.95 and 4) from base temperature to above their Neel temperatures. Their magnetic structures were analysed by using the irreducible representation analysis and Rietveld refinement method. Similar to Co4Nb2O9, the compounds with x  ⩽  3.9 have noncollinear in-plane magnetic structures (Γ6) with magnetic moments lying purely in the ab plane with certain canting angles. Mn4Nb2O9 has a collinear antiferromagnetic structure (Γ2) with magnetic moments aligning along the c axis. The compound of x  =  3.95 shows two magnetic phases in the magnetization, which was confirmed to have the Γ2 magnetic structure above 60 K and develop a second Γ6 local phase in addition to the main Γ2 phase due to doping. This study indicates 2.5 at% Co2+ doping is sufficient to alter the collinear easy-axis magnetic structure of Mn4Nb2O9 into the noncollinear easy-plane magnetic structure, which is attributed to the large easy-plane anisotropy of Co2+ and relative small Ising-like anisotropy of Mn2+. The doping effects on the Néel temperature and occupancy are also discussed. © 2019 IOP Publishing Ltd
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    Tuning the magnetic anisotropy via Mn substitution in single crystal Co4Nb2O9
    (Elsevier, 2019-01-01) Yu, YS; Deng, GC; Cao, YM; McIntyre, GJ; Li, RB; Yuan, N; Feng, ZJ; Ge, JY; Zhang, JC; Cao, SX
    By using the optical floating-zone technique to grow a series of high-quality Co4-xMnxNb2O9 single crystals, the effect of Mn doping on the magnetic anisotropy and spin-flop is investigated. The antiferromagnetic phase transition and spin-flop transition for these samples (x ≤ 3.9) are similar to those in the parent phase of Co4Nb2O9, revealing that Co2+ ions in Co4-xMnxNb2O9 possess a strong single-ion anisotropy. The critical doping content, above which the magnetic anisotropy changes from easy-plane to easy-axis, has been identified as x = 3.95 with an additional kink observed in the magnetization curve below the N é el temperature. A spin-flop transition is reported for the first time in Mn4Nb2O9 at a field of 10.9 T at 2 K. © 2018 Elsevier Ltd and Techna Group S.r.l.
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    Unlocking anionic redox activity in O3-type sodium 3d layered oxides via Li substitution
    (Springer Nature, 2021-01-11) lorem, Ipsum; Wang, Q; Mariyappan, S; Rousse, G; Morozov, AV; Porcheron, B; Dedryvère, R; Wu, JP; Yang, WL; Zhang, LT; Chakir, M; Avdeev, M; Deschamps, M; Yu, YS; Cabana, J; Doublet, ML; Abakumov, AM; Tarascon, JM
    Sodium ion batteries, because of their sustainability attributes, could be an attractive alternative to Li-ion technology for specific applications. However, it remains challenging to design high energy density and moisture stable Na-based positive electrodes. Here, we report an O3-type NaLi1/3Mn2/3O2 phase showing anionic redox activity, obtained through a ceramic process by carefully adjusting synthesis conditions and stoichiometry. This phase shows a sustained reversible capacity of 190 mAh g−1 that is rooted in cumulative oxygen and manganese redox processes as deduced by combined spectroscopy techniques. Unlike many other anionic redox layered oxides so far reported, O3-NaLi1/3Mn2/3O2 electrodes do not show discernible voltage fade on cycling. This finding, rationalized by density functional theory, sheds light on the role of inter- versus intralayer 3d cationic migration in ruling voltage fade in anionic redox electrodes. Another practical asset of this material stems from its moisture stability, hence facilitating its handling and electrode processing. Overall, this work offers future directions towards designing highly performing sodium electrodes for advanced Na-ion batteries. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.