Browsing by Author "Feng, ZJ"

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    Giant shifts of crystal-field excitations in ErFeO3 driven by internal magnetic fields
    (Cornell University, 2021-09-16) O'Brien, J; Deng, GC; Ma, XX; Feng, ZJ; Ren, W; Cao, SX; Yu, DH; McIntyre, GJ; Ulrich, C
    Crystal-field excitations in transition-metal oxides where -rare-earth elements locate in the space between the transition-metal-oxide tetrahedra and octahedra, are assumed to be robust with respect to external perturbations such as temperature. Using inelastic neutron-scattering experiments, a giant shift of the energy of the lowest crystal-field excitation of Er3+ (4I15/2) in ErFeO3 from 0.35 meV to 0.75 meV was observed on cooling from 10K to 1.5K through the magnetic ordering temperature of Er3+ at 4.1 K. A crystal-field model was proposed to explain the observed crystal field excitations in this work. The model indicates the lowest-energy crystal-field excitation in ErFeO3 is the first Kramers doublet above the ground state. Its energy substantially shifts by the internal field induced by the ordered Er3+ magnetic moments. Further magnetic-field-dependent measurements provide strong supportive evidence for this scenario. By fitting the external magnetic-field dependency of the crystal-field excitation energy, the internal field generated by Er3+ magnetic moments was derived to be ~0.33meV. The result indicates that the internal field of Er3+ magnetic moments contribute to the energy shift of the crystal-field excitations. The giant energy shift under fields could be attributed to the anisotropy of the large effective g-factor. CC BY: Creative Commons Attribution
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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.