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PubMed | Chinese Academy of Sciences, Renmin University of China, CAS Institute of High Energy Physics, Wuhan National High Magnetic Field Center and 3 more.
Type: | Journal: Scientific reports | Year: 2015

Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60mK (despite w~-4K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (|w|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures.

Ren X.,Huazhong University of Science and Technology | Zhang X.,Huazhong University of Science and Technology | Zhang X.,Hubei University | Liu N.,Huazhong University of Science and Technology | And 8 more authors.
Advanced Functional Materials | Year: 2015

A whole interfacial transition of electrons from conduction bands of n-type material to the acceptor levels of p-type material makes the energy band engineering successful. It tunes intrinsic ZnO UV emission to UV-free and warm white light-emitting diode (W-LED) emission with color coordinates around (0.418, 0.429) at the bias of 8-15.5 V. The W-LED is fabricated based on antimony (Sb) doped p-ZnO nanowire arrays/Si doped n-GaN film heterojunction structure through one-step chemical vapor deposition with quenching process. Element analysis shows that the doping concentration of Sb is ≈1.0%. The I-V test exhibits the formation of p-type ZnO nanowires, and the temperature-dependent photoluminescence measurement down to 4.65 K confirms the formation of deep levels and shallow acceptor levels after Sb-doping. The intrinsic UV emission of ZnO at room temperature is cut off in electroluminescence emission at a bias of 4-15.5 V. The UV-free and warm W-LED have great potential application in green lights program, especially in eye-protected lamp and display since television, computer, smart phone, and mobile digital equipment are widely and heavily used in modern human life, as more than 3000 h per year. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Li Y.,Renmin University of China | Pan B.,Fudan University | Li S.,Fudan University | Tong W.,CAS Hefei Institutes of Physical Science | And 6 more authors.
New Journal of Physics | Year: 2014

We have successfully synthesized the new S = 1/2 anisotropic kagome antiferromagnet ZnCu3(OH)6SO4 and determined its structure by synchrotron x-ray diffraction. No magnetic ordering is observed down to 50 mK, despite a moderately high Weiss temperature of Θw∼ -79 K, indicating that the compound is a new quantum spin liquid (QSL) candidate. A linear temperature dependence of the magnetic heat capacity is found at 6 ∼ 15 K and below 0.6 K. Temperature-independent intrinsic susceptibilities are observed exactly in both temperature ranges. This consistently suggests a gapless QSL below 0.6 K, which may evolve from an unconventional quantum spin state at higher temperatures (6 ∼ 15 K). © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

While the applications of this discovery remain to be seen, this represents a significant breakthrough in fundamental physics. It could inspire work in high-energy physics, such as the collision experiments carried out in particle accelerators like CERN. This is the third joint publication between the group in Trinity and Prof. Faxian Xiu at Fudan University in Shanghai, who approached Prof Sanvito to provide theory support for their experimental activity based on his previous publications and international reputation in the field of theoretical physics. Prof Stefano Sanvito, Principal Investigator at the Science Foundation Ireland funded AMBER (Advanced Materials and BioEngineering Research) centre based at Trinity and the CRANN Institute and Professor in Trinity's School of Physics said, "This is a very exciting breakthrough because until now, nobody has ever discovered an object whose mass can be switched on or off by applying an external stimulus. Every physical object has a mass, which is a measure of the object's resistance to a change in its direction or speed, once a force is applied. While we can easily push a light-mass shopping trolley, we cannot move a heavy-mass 6-wheel lorry by simply pushing. However, there are some examples in Nature of objects not having a mass. These include photons, the elementary particles discovered by Einstein responsible for carrying light, and neutrinos, produced in the sun as a result of thermonuclear reactions. We have demonstrated for the first time one way in which mass can be generated in a material. In principle the external stimulus that enabled this, the magnetic field, could be replaced with some other stimulus and perhaps applied long-term in the development of more sophisticated sensors or actuators. It is impossible to say what this could mean, but like any fundamental discovery in physics, the importance is in its discovery." He continued, "It has been very satisfying to continue to work with Prof Xiu in Shanghai. While his group are experts in growing and characterizing materials such as ZrTe5 which are very difficult to make, my group has the expertise in the theoretical interpretation. The measurements were carried out in Fudan and at the Wuhan National High Magnetic Field Center in China, while the Dublin team provided the theoretical explanation for the finding. This has been a very fruitful collaboration and we have a number of other publications in progress". The team studied what happened to the current passing through the exotic material zirconium pentatelluride (ZrTe5) when exposed to a very high magnetic field. Measuring a current in a high magnetic field is a standard way of characterising the material's electronic structure. In the absence of a magnetic field the current flows easily through ZrTe5. This is because in ZrTe5 the electrons responsible for the current have no mass. However, when a magnetic field of 60 Tesla is applied (a million times more intense than the earth's magnetic field) the current is drastically reduced and the electrons acquire a mass. An intense magnetic field in ZrTe5 transforms slim and fast electrons into fat and slow ones. Explore further: Scientists explain the theory behind Ising superconductivity More information: Yanwen Liu et al, Zeeman splitting and dynamical mass generation in Dirac semimetal ZrTe5, Nature Communications (2016). DOI: 10.1038/ncomms12516

Tong F.,Hong Kong Polytechnic University | Tong F.,Huazhong University of Science and Technology | Tong F.,Wuhan National Laboratory for Optoelectronics | Hao J.H.,Hong Kong Polytechnic University | And 5 more authors.
Applied Physics Letters | Year: 2011

Phase change control of ferromagnetism in Ge0.98Fe 0.02Te thin film prepared by pulsed laser deposition is investigated. The magnetic property of Fe doped phase change material GeTe is found to vary with phase change between amorphous and crystalline states corresponding to the variation of conductance during phase change. The results indicate that a fast control of ferromagnetism by phase change can be realized. The measurement of temperature dependent magnetization shows a long range ferromagnetic interaction in ordered crystalline phase and a short range ferromagnetic interaction in frustrated amorphous phase, which is consistent with phase change. © 2011 American Institute of Physics.

Hui Y.,Huazhong University of Science and Technology | Hui Y.,Wuhan National Laboratory for Optoelectronics | Cheng W.,Huazhong University of Science and Technology | Cheng W.,Wuhan National Laboratory for Optoelectronics | And 5 more authors.
Journal of Electronic Materials | Year: 2014

A sputter-deposited strontium ferrite film with perpendicular anisotropy has been developed. The film, composed of La0.33Sr 0.67Co0.25Fe11.75O19, has been fabricated directly on quartz glass substrates by radio frequency magnetron sputtering with various heat treatments. The structural and magnetic property dependence of those films on heat treatments has also been studied. The optimized condition is the heat treatment of in situ heating at 400°C and post-annealing at 850°C-900°C. When post-annealing temperature exceeds 900°C, parasitic phases of γ-Fe2O3 and LaFeO3 appear and gradually increase; meanwhile, the magneto plumbite phase gradually decreases. High c-axis perpendicularly oriented films with the coercivity (4148 Oe), remanence squareness ratio (0.89) and perpendicular magnetic anisotropy energy density (1.65 × 106 erg/cm 3) are achieved, which is attributed to the single magneto plumbite phase with compact platelet grains and almost complete (0 0 l) texture of the c-axis normal to the film plane. © 2014 TMS.

Tong F.,Huazhong University of Science and Technology | Tong F.,Wuhan National Laboratory for Optoelectronics | Miao X.S.,Huazhong University of Science and Technology | Miao X.S.,Wuhan National Laboratory for Optoelectronics | And 7 more authors.
Applied Physics Letters | Year: 2010

X-ray diffraction and photoelectron spectroscopy of different Co-doped concentration GeTe have been made to identify the vacancies in rock-salt GeTe. The results show that Co occupies germanium vacancy and forms Co-Te bond, but the alloy retains a rock-salt structure when the concentration of doped Co is less than the vacancy ratio in crystalline GeTe. If we construct 8% germanium vacancy and relative distortion in rock-salt GeTe, the magnetism calculation based on spin-polarized density functional theory of Co-doped GeTe agrees well with superconducting quantum interference device magnetometer result. From experiment and calculation results, we can confirm the existence of vacancies in rock-salt GeTe and the ratio is 8%. © 2010 American Institute of Physics.

Ju C.,Wuhan National Laboratory for Optoelectronics | Ju C.,Huazhong University of Science and Technology | Cheng X.M.,Wuhan National Laboratory for Optoelectronics | Cheng X.M.,Huazhong University of Science and Technology | And 3 more authors.
Applied Physics Letters | Year: 2012

Si doping is proposed to be an effective way to improve the amorphous stability of Bi 2Te 3 thin film. Structural changes in doped crystalline phases are revealed by the bonding nature given by x-ray photoelectron spectroscopy results. Based on ab initio simulations, the energy, electronic and structural changes induced by Si doping are studied. The results show that both nucleation and growth of crystallite are suppressed by Si doping, so that the stability of amorphous Bi 2Te 3 is improved. © 2012 American Institute of Physics.

Cheng W.,Huazhong University of Science and Technology | Dai Y.,Huazhong University of Science and Technology | Hu H.,Huazhong University of Science and Technology | Cheng X.,Huazhong University of Science and Technology | And 2 more authors.
Journal of Electronic Materials | Year: 2012

SmCo5 film with perpendicular magnetic anisotropy is a promising candidate ultrahigh-density magnetic recording medium due to its huge magnetocrystalline anisotropy. This paper investigates the effect of Cu substitution for Co on the magnetic properties and microstructure of SmCo 5 film by simulations and experiments. The simulation results based on first-principles theory show that Cu substitution for Co in SmCo5 can reduce the total exchange- correlation constant and increase the coercivity of SmCo5 film. Sm(Co,Cu)5/Cu/TiW film samples with different Cu doping were fabricated on quartz glass substrates by radiofrequency (RF) magnetron sputtering, and the dependence of the coercivity of the Sm(Co,Cu)5 film on the Cu doping and annealing conditions was studied. The experimental results demonstrate that Cu doping can decrease the grain size and increase the coercivity of SmCo5 film. By optimizing the sputtering and annealing conditions, perpendicular coercivity of 3796 Oe was obtained in Sm(Co0.72Cu0.28)5 film. © 2012 TMS.

Peng T.,Wuhan National High Magnetic Field Center | Sun Q.Q.,Wuhan National High Magnetic Field Center | Zhang X.,Wuhan National High Magnetic Field Center | Xu Q.,Wuhan National High Magnetic Field Center | And 4 more authors.
Journal of Low Temperature Physics | Year: 2013

The first 80 T dual-coil magnet was manufactured and tested at the Wuhan National High Magnetic Field Center (WHMFC). The inner coil consists of 8 layers of 2.8 mm × 4.3 mm CuNb microcomposite wire developed in China; the bore diameter is 14 mm and the outer diameter 135 mm. The outer coil was wound directly on the inner coil with 12 layers of 3 mm × 6 mm soft copper. Each conductor layer of both coils was reinforced by Zylon/epoxy composite. The inner and outer coil were driven by a 1.6 MJ/5.12 mF capacitor bank and by eight 1 MJ/3.2 mF modules, respectively. At the voltage of 14.3 kV for the inner coil and 22 kV for the outer coil, the inner and outer coils produced peak fields of 48.5 T and 34.5 T respectively, which gave a total field of 83 T. This was the first combined operation of the new capacitor banks installed at the WHMFC. We present details of the design, manufacture and test of the dual-coil magnet and discuss crucial material properties. Based on this experience, a second dual-coil magnet will be designed; the enhanced design will be discussed. With the total energy of 12.6 MJ, peak field up to 90 T is expected. © 2012 Springer Science+Business Media, LLC.

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