Browsing by Author "Zheng, RK"
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- ItemGiant linear magnetoresistance in half-metallic Sr2CrMoO6 thin films(Springer Nature, 2021-12-01) Wang, ZC; Chen, L; Li, SS; Ying, JS; Tang, F; Gao, GY; Fang, Y; Zhao, WY; Cortie, DL; Wang, XL; Zheng, RKLinear magnetoresistance (LMR) is a special case of a magnetic-field induced resistivity response, which has been reported in highly disordered semiconductor systems and in topological materials. In this work, we observe LMR effect in half-metallic perovskite Sr2CrMoO6 thin films, of which the maximum MR value exceeds +1600% at 2 K and 14 T. It is an unusual behavior in ferrimagnetic double perovskite material like Sr2CrMoO6, which are known for intrinsic tunneling-type negative magnetoresistance. In the thin films, the high carriers’ density (~1022 cm−3) and ultrahigh mobility (~104 cm2 V−1 s−1) provide a low-resistivity (~10 nΩ·cm) platform for spin-polarized current. Our DFT calculations and magnetic measurements further support the half-metal band structure. The LMR effect in Sr2CrMoO6 could possibly originate from transport behavior that is governed by the guiding center motion of cyclotron orbitals, where the magnetic domain structure possibly provides disordered potential. The ultrahigh mobility and LMR in this system could broaden the applications of perovskites, and introduce more research on metallic oxide ferri-/ferro-magnetic materials. © The Author(s) 2021 - Open Access CC BY licence.
- ItemGraphene doping to enhance the flux pinning and supercurrent carrying ability of a magnesium diboride superconductor(Institute of Physics, 2010-08) Xu, X; Dou, SX; Wang, XL; Kim, JH; Stride, JA; Choucair, M; Yeoh, WK; Zheng, RK; Ringer, SPThe effect of graphene doping on the electromagnetic properties of MgB2 has been examined, in comparison with the case for undoped MgB2. It was found that graphene doping is more efficient than other forms of carbon doping for effecting improvement in the critical current density–field performance (Jc(B)), with little change in the transition temperature of MgB2. An optimal enhancement of Jc(B) was achieved for 3.7 at.% graphene doped MgB2, by a factor of 30 at 5 K and 10 T, as compared to undoped MgB2. It is found that spatial fluctuation in Tc is responsible for the flux pinning mechanism of graphene doped MgB2. © 2010, Institute of Physics
- ItemAn investigation of LnUO4 (Ln = Dy and Ho): structures, microstructures, uranium valences and magnetic properties(Elsevier, 2021-09-12) Lu, KT; Zhang, YJ; Wei, T; Zhang, ZM; Avdeev, M; Zheng, RKThe phase formation, structures, microstructures, uranium valences and magnetic properties of LnUO4 (Ln = Dy and Ho) were investigated. Although sintering of the precursors in argon at 1450 °C for seven days and 1400 °C for six hours both resulted in the desired phase, sintering at higher temperature for longer duration led to the formations of well crystalized lanthanide monouranates with much better homogeneity. Cubic fluorite structures were determined using X-ray diffraction data, which was confirmed with transmission electron microscopy and Raman spectroscopy. The nature of pentavalent uranium was verified with a combination of diffuse reflectance and X-ray photoelectron spectroscopies. The magnetic suseptability measurements revealed that they are paramagnetic with no long-range magnetic orders, likely due to the extensive short-range oxygen defects. Overall the improved structural and spectroscopic understandings of LnUO4 have implications in nuclear materials especially for potential accident tolerance fuels and spent fuel management. Crown Copyright © 2021 Published by Elsevier Ltd.
- ItemA large spin-crossover [Fe4L4]8+ tetrahedral cage(Royal Society of Chemistry, 2015-05-20) Li, L; Saigo, N; Zhang, YJ; Fanna, DJ; Shepherd, ND; Clegg, JK; Zheng, RK; Hayami, S; Lindoy, LF; Aldrich-Wright, JR; Li, CG; Reynolds, JK; Harman, DG; Li, FA large discrete face-capped tetranuclear iron(II) cage, [Fe4L4](BF4)8·n(solvent), was synthesised via metal-ion directed self-assembly. The cage is formed from a rigid tritopic ligand that incorporates chelating imidazole-imine functional groups. The cage displays temperature induced spin-crossover and LIESST effects and is amongst the largest iron(II) tetrahedral cages with such properties reported. The synthesis, structure and magnetic properties of this new metallo-cage are presented. © 2015 The Royal Society of Chemistry
- ItemMagnetotransport and Berry phase tuning in Gd-doped Bi2Se3 topological insulator single crystals(American Physical Society, 2022-05-01) Chen, L; Li, SS; Zhao, W; Bake, A; Cortie, DL; Wang, XL; Karel, J; Li, H; Zheng, RKThe Berry phase is an important concept in solids, correlated to the band topology, axion electrodynamics, and potential applications of topological materials. Here, we investigate the magnetotransport and Berry phase of rare earth element Gd-doped Bi2Se3 (Gd:Bi2Se3) topological insulators (TIs) at low temperatures and high magnetic fields. Gd:Bi2Se3 single crystals show Shubnikov-de Haas (SdH) oscillations with nontrivial Berry phase, while Bi2Se3 single crystals show zero Berry phase in SdH oscillations. A fitting of the temperature-dependent magnetization curves using the Curie-Weiss law reveals that the Gd dopants in the crystals show paramagnetism in the 3-300 K region, indicating that the origin of the Berry phase is not long-range magnetic ordering. Moreover, Gd doping has limited influence on the quantum oscillation parameters (e.g., frequency of oscillation, area of Fermi surface, effective electron mass, and Fermi wave vectors) but has a significant impact on the Hall mobility, carrier density, and band topology. Our results demonstrate that Gd doping can tune the Berry phase of TIs effectively, which may pave the way for the future realization of many predicted exotic transport phenomena of topological origin. ©2022 American Physical Society
- ItemSelf-assembly of a unique 3d/4f heterometallic square prismatic box-like coordination cage(Royal Society of Chemistry, 2016-05-23) Li, L; Zhang, Y; Avdeev, M; Lindoy, LF; Harman, DG; Zheng, RK; Cheng, Z; Aldrich-Wright, JR; Li, FAbstractWe present the synthesis and characterization of a unique, slightly distorted square prismatic, box-like coordination cage of type [Cu6Dy8L8(MeOH)8(H2O)6](NO3)12·χsolvent obtained via the supramolecular assembly between a non-centrosymmetric Dy(III) metalloligand and Cu(II) nitrate. Magnetic susceptibility measurements indicate that the complex behaves as a single-molecule magnet. © 2016 Royal Society of Chemistry
- ItemSpin reorientation transition and negative magnetoresistance in ferromagnetic NdCrSb3 single crystals(MDPI, 2023-02-20) Chen, L; Zhao, WY; Wang, ZC; Tang, F; Fang, Y; Zeng, Z; Xia, ZC; Cheng, ZX; Cortie, DL; Rule, KC; Wang, XL; Zheng, RKHigh-quality NdCrSb3 single crystals are grown using a Sn-flux method, for electronic transport and magnetic structure study. Ferromagnetic ordering of the Nd3+ and Cr3+ magnetic sublattices are observed at different temperatures and along different crystallographic axes. Due to the Dzyaloshinskii–Moriya interaction between the two magnetic sublattices, the Cr moments rotate from the b axis to the a axis upon cooling, resulting in a spin reorientation (SR) transition. The SR transition is reflected by the temperature-dependent magnetization curves, e.g., the Cr moments rotate from the b axis to the a axis with cooling from 20 to 9 K, leading to a decrease in the b-axis magnetization f and an increase in the a-axis magnetization. Our elastic neutron scattering along the a axis shows decreasing intensity of magnetic (300) peak upon cooling from 20 K, supporting the SR transition. Although the magnetization of two magnetic sublattices favours different crystallographic axes and shows significant anisotropy in magnetic and transport behaviours, their moments are all aligned to the field direction at sufficiently large fields (30 T). Moreover, the magnetic structure within the SR transition region is relatively fragile, which results in negative magnetoresistance by applying magnetic fields along either a or b axis. The metallic NdCrSb3 single crystal with two ferromagnetic sublattices is an ideal system to study the magnetic interactions, as well as their influences on the electronic transport properties. © 2023 The Authors, Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.
- ItemStress/strain induced flux pinning in highly dense MgB2 bulks(Institute of Electrical and Electronics Engineers (IEEE), 2009-06-01) Zeng, R; Dou, SX; Lu, L; Li, WX; Poh, CK; Kim, JH; Horvat, J; Shi, DQ; Wang, JL; Munroe, P; Wang, XF; Zheng, RK; Ringer, SP; Rindfleisch, M; Tomsic, MWe have systematically studied the flux pinning behavior of MgB(2) bulks synthesized by direct diffusion of Mg into pressed pellets of high purity crystalline B powder, with and without mixing with C and SiC nanoparticles, at a reaction temperature of 850 degrees C for 10 hrs. All of the samples showed very high purity and high density, but their microstructure and flux pinning behavior showed significant differences. It was found that the pure MgB(2) agrees with the delta T(c) pinning model, nano-C doped MgB(2) agrees with the delta l pinning model, while the SiC + MgB(2) composite agrees with the delta epsilon pinning model (stress/strain field pinning), since the dominant micro-defects that influence the flux pinning in these three samples are different. © 2009, Institute of Electrical and Electronics Engineers (IEEE)
- ItemTopological insulator VxBi1.08-x Sn0.02Sb0.9Te2S as a promising n-type thermoelectric material(Elsevier, 2022-10) Chen, L; Zhao, WY; Li, M; Yang, G; Guo, L; Bake, A; Liu, P; Cortie, DL; Zheng, RK; Cheng, ZX; Wang, XLAs one of the most important n-type thermoelectric (TE) materials, Bi2Te3 has been studied for decades, with efforts to enhance the thermoelectric performance based on element doping, band engineering, etc. In this study, we report a novel bulk-insulating topological material system as a replacement for n-type Bi2Te3 materials: V doped Bi1.08Sn0.02Sb0.9Te2S (V:BSSTS). The V:BSSTS is a bulk insulator with robust metallic topological surface states. Furthermore, the bulk band gap can be tuned by the doping level of V, which is verified by magnetotransport measurements. Large linear magnetoresistance is observed in all samples. Excellent thermoelectric performance is obtained in the V:BSSTS samples, e.g., the highest figure of merit ZT of ~ 0.8 is achieved in the 2% V doped sample (denoted as V0.02) at 530 K. The high thermoelectric performance of V:BSSTS can be attributed to two synergistic effects: (1) the low conductive secondary phases Sb2S3, and V2S3 are believed to be important scattering centers for phonons, leading to lower lattice thermal conductivity; and (2) the electrical conductivity is increased due to the high-mobility topological surface states at the boundaries. In addition, by replacing one third of costly tellurium with abundant, low-cost, and less-toxic sulfur element, the newly produced BSSTS material is inexpensive but still has comparable TE performance to the traditional Bi2Te3-based materials, which offers a cheaper plan for the electronics and thermoelectric industries. Our results demonstrate that topological materials with unique band structures can provide a new platform in the search for new high performance TE materials. © 2022 Elsevier B.V.