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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. Source

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. Source

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. Source

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. Source

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

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