Browsing by Author "Cao, YM"
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- ItemLarge 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, GJNeutron 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
- ItemMagnetic structure and spin dynamics of multiferroic system Co4Nb2O9(Australian Institute of Physics, 2017-02-01) Deng, GC; Cao, YM; Ren, W; Cao, SX; Gauthier, N; Kenzelmann, M; Studer, AJ; Rule, KC; Gardner, JS; Davison, G; Imperia, P; McIntyre, GJCo4Nb2O9, was recently reported to have large magneto-dielectric coupling effect under a certain magnetic field. This compound has a corundum-type crystal structure of space group P-3c1 of ref. and undergoes antiferromagnetic phase transition around 27 K. It was previously believed that the magnetic moments of Co2+ order into a collinear antiferromagnetic structure in which Co2+ spins order parallel to the c-direction and form ferromagnetic chains with antiparallel inter-chain coupling. However, the recent study has shown that this magnetic structure model is incorrect. In this study, we found that the Co2+ magnetic moments align in the ab plane with a non-collinear configuration. Using inelastic neutron scattering, we measured the spin wave excitation from its magnetic phase along (h00) and (00l). A magnetic model was proposed to explain the observed spin dynamical behavior. There are two inequivalent Co sites, which form spin chains in an alternative way along c axis. Each Co2+ moment couples with its two inequivalent neighbors on the same chain with ferromagnetic interactions. Co2+ moments from each site form a zig-zag hexagonal ring perpendicular to the c axis, where antiferromagnetic interactions dominate. On the basis of this model, the observed spin wave spectra can be well simulated by SpinW.
- ItemOrigin of magnetoelectric coupling effect and spin dynamics of multiferroic system Co4Nb2O9(International Conference on Neutron Scattering, 2017-07-12) Deng, GC; Cao, YM; Ren, W; Cao, SX; Studer, AJ; Gauthier, N; Kenzelmann, M; Davison, G; Rule, KC; Gardner, JS; Imperia, P; Ulrich, C; McIntyre, GJCo4Nb2O9,was recently reported to have large magnetoelectric coupling effect under a certain magnetic field. This compound has a crystal structure (space group P-3c1) derived from corundum structure and undergoes antiferromagnetic phase transition around 27K. It was previously believed that the magnetic moments of Co2+ order into a collinear antiferromagnetic structure in which magnetic moments are parallel to the c axis and form ferromagnetic chains with antiparallel inter-chain coupling. However, the recent study has shown that this magnetic structure model is incorrect. In this study, we found that the Co2+magnetic moments on both Co1 and Co2 sites align in the ab plane with a non-collinear configuration. Using inelastic neutron scattering, we measured the spin wave excitation from its magnetic phase along (h00) and (00l). A spin dynamic model proposed in this study is able to explain the observed spin dynamical behavior quite well. The nearest and next nearest neighbor interactions (NN and NNN) along the c axis are ferromagnetic. The interaction on the zig-zag ring of Co1 perpendicular to the c axis is highly frustrated while that of the zig-zag ring of Co2 is antiferromagnetic. The single ion anisotropy and Dzyaloshinskii-Moriya (DM) interaction contribute to the spin dynamics of Co4Nb2O9 as well. The simulated spin wave excitation by using SpinW[5] matches the experimental data very well. The DM interaction, which is most probably due to the triangle Co2-O-Co2 bond, was found to be the origin of the magnetoelectric coupling in this compound.
- ItemSpin dynamics and magnetoelectric coupling mechanism of Co4Nb2O9(American Physical Society, 2018-02-28) Deng, GC; Cao, YM; Ren, W; Cao, SX; Studer, AJ; Gauthier, N; Kenzelmann, M; Davidson, G; Rule, KC; Gardner, JS; Imperia, P; Ulrich, C; McIntyre, GJNeutron powder diffraction experiments reveal that Co4Nb2O9 forms a noncollinear in-plane magnetic structure with Co2+ moments lying in the ab plane. The spin-wave excitations of this magnet were measured by using inelastic neutron scattering and soundly simulated by a dynamic model involving nearest- and next-nearest-neighbor exchange interactions, in-plane anisotropy, and the Dzyaloshinskii-Moriya interaction. The in-plane magnetic structure of Co4Nb2O9 is attributed to the large in-plane anisotropy, while the noncollinearity of the spin configuration is attributed to the Dzyaloshinskii-Moriya interaction. The high magnetoelectric coupling effect of Co4Nb2O9 in fields can be explained by its special in-plane magnetic structure. ©2018 American Physical Society
- ItemTuning 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, SXBy 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.