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Now showing items 1 - 16 of 1576

  • The magnetic origin of multiferroic Y2CoMnO6

    Jia, Ting   Zeng, Zhi   Li, X. G.   Lin, H. Q.  

    It has been found experimentally that the ferroelectricity in Y2CoMnO6 is driven by a magnetic ordering of collinear up-up-down-down (up arrow up arrow down arrow down arrow). Here, the origin of the magnetism and thereby ferroelectricity is studied using first-principles calculations. We first confirm that the experimentally observed up arrow up arrow down arrow down arrow antiferromagnetic structure is the ground state of Y2CoMnO6. Additionally, both the Co2+ and Mn4+ are in the high-spin state. By analyzing the exchange coupling and corresponding pathways, we conclude that the up arrow up arrow down arrow down arrow spin order in Y2CoMnO6 originates from a subtle competition between the ferromagnetic Co-O-Mn super-exchange and antiferromagnetic Co-Mn direct-exchange along c axis. (C) 2015 AIP Publishing LLC.
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  • Optical properties of impact diamonds from the Popigai astrobleme

    Yelisseyev, A.   Meng, G. S.   Afanasyev, V.   Pokhilenko, N.   Pustovarov, V.   Isakova, A.   Lin, Z. S.   Lin, H. Q.  

    Impact diamonds from Popigai astrobleme were found to consist of different carbon phases: cubic and hexagonal diamond with sp(3) bonding according to X-ray structural analysis as well as amorphous, crystalline and disordered graphite with sp(2)-bonding (Raman scattering). The sizes of graphite domains vary from 10 to 100 nm. Fundamental absorption edge for Popigai impact diamonds is shifted similar to 0.5 eV to lower energies in comparison with kimberlite diamonds (5.47 eV) as a result of the lonsdaleite input, in good agreement with ab initio calculations (E-g = 534 and 4.55 eV for 3C cubic and 2H hexagonal diamonds, respectively). Yellowish color of impact diamonds is due to Rayleigh light scattering on structural defects whereas graphite is responsible for gray to black coloring. In the mid-IR region there is a multi-phonon absorption of 3C diamond in the 1800 to 2800 cm(-1) range and some new bands at 969, 1102, 1225, and 1330 cm(-1) in the one-phonon region. Micro-Raman study shows inclusions of side noncarbon minerals (quartz, magnetite, and hematite) some of which contain Cr3+ impurity. The vibration modes of cubic diamond and lonsdaleite exhibited in the Raman spectra were elucidated by the first-principles studies. Popigai impact diamonds demonstrate a broad-band luminescence in 2.1, 2.38, and 2.84 eV components similar to that for nanocrystal polycrystalline 3C diamond. All emissions are excited at band-to-band transitions whereas the last two are observed also at excitation into 2.4 and 3.0 bands supposedly as a result of intracenter processes within the H3(NVN) and NV0 centers. (C) 2013 Elsevier B.V. All rights reserved.
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  • Indirect exchange of magnetic impurities in zigzag graphene ribbon

    Sun, J. H.   Hu, F. M.   Tang, H. K.   Guo, W.   Lin, H. Q.  

    We use quantum Monte Carlo method to study the indirect coupling between two magnetic impurities on the zigzag edge of graphene ribbon. If the two adatoms are located on the sites belonging to opposite sublattices, their antiferromagnetic spin-spin correlation is drastically suppressed at the zero-energy, and is first enhanced and then decreased as we lower the chemical potential. If the two adatoms are adsorbed on the same sublattice, we find similar behavior of spin-spin correlation except for a crossover from ferromagnetic to antiferromagnetic correlation as we lower the chemical potential. We also calculate the weight of different components of d-electron wave function and local magnet moment for various values of parameters, and all the results are consistent with those of spin-spin correlation between two magnetic impurities. (C) 2013 American Institute of Physics.
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  • Spin-flip effect on transport properties of a Mn-3 molecule

    Hao, Hua   Zheng, XiaoHong   Wang, RuiNing   Zeng, Zhi   Lin, H. Q.  

    Electron transport through a single-molecule magnet [NEt4](3)[Mn3Zn2(salox)(3)O(N-3)(6)Cl-2] is investigated by spin-polarized density functional theory combined with the Keldysh nonequilibrium Green's function technique. Our study demonstrates that spin-filtering effect and negative differential resistance exist in the ground state of this molecule. When the magnetic state of the molecule is changed from its ground state to the spin-flip state, substantial changes are induced not only in energy levels of the molecule, but also in the coupling of molecular states with eigenstates of Ag(100) nano-electrodes, which lead to the disappearance of spin-filtering effect and negative differential resistance. (C) 2012 American Institute of Physics. [doi:10.1063/1.3670984]
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  • Electronic structure and magnetism of La4Ni3O8 from first principles

    Liu, Ting   Zhang, Guoren   Zhang, Xiaoli   Jia, Ting   Zeng, Zhi   Lin, H. Q.  

    The magnetic and electronic properties of La4Ni3O8 are investigated by performing the full-potential linearized augmented plane wave method. The C-type antiferromagnetic spin ordering is preferred and a molecular correlated insulating state with high-spin Ni ions is found. Our results have proved that this insulating state is caused by a correlation effect and the strong interlayer interaction. Such strong interlayer coupling results from the high-spin occupation of Ni ions.
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  • Magnetic frustration in alpha-NaMnO(2) and CuMnO(2)

    Jia, Ting   Zhang, Guoren   Zhang, Xiaoli   Guo, Ying   Zeng, Zhi   Lin, H. Q.  

    The magnetic and electronic properties of alpha-NaMnO(2) and delafossite CuMnO(2) are investigated using a full-potential linearized augmented plane wave method. For the monoclinic structure at room temperature, CuMnO(2) behaves like a frustrated spin-lattice. For the triclinic structure at low temperature, the obtained magnetic configurations of the lowest energy for both alpha-NaMnO(2) and CuMnO(2) are consistent with experiments. However, the exchange constants are all positive. This reveals that the magnetic frustration is only partially relieved at low temperature. It is also found that the Mn(3+) ions are in a high-spin state. Taking into account the on-site Coulomb correlations, our results show that alpha-NaMnO(2) and CuMnO(2) are charge-transfer insulators. (C) 2011 American Institute of Physics. [doi:10.1063/1.3536533]
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  • Investigation of pressure effects on Mn(x)Ge(1-x)

    Wang, X. L.   Ni, M. Y.   Zeng, Z.   Lin, H. Q.  

    In the present work, the pressure effects on the electronic and magnetic properties of Mn(x)Ge(1-x) semiconductor have been investigated. The obtained results show that the lattice constant of Mn(x)Ge(1-x) increases with the Mn concentration increase. The magnetic moments of Mn ions decrease with increasing pressure. The interactions between Mn ions is a Ruderman-Kittel-Kasuya-Yosida like one over the whole pressure range applied. The role of the pressure actually increases the intensity of the interactions, and consequently the Curie temperature of Mn-doped Ge system increases with the pressure increase. (C) 2009 Elsevier B. V. All rights reserved.
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  • Magnetic and electronic properties of alpha-NaMnO(2)

    Zhang, G. R.   Zou, L. J.   Zeng, Z.   Lin, H. Q.  

    The magnetic and electronic properties of alpha-NaMnO(2) are investigated by performing the first-principles density functional calculations. A semiconducting ground state with high spin Mn is found. The magnetic coupling within a Mn layer is antiferromagnetic and frustrated, while the coupling between layers is very weak. Spatially anisotropic exchange is found within a Mn layer. The large Jahn-Teller distortion lowers the energy of d(3r2-z2) orbital, leading to the stabilization of high spin Mn and ferromagnetic orbital ordering. Moreover, GGA+U studies show that alpha-NaMnO(2) has the mixed characteristics of Mott-Hubbard insulators and charge transfer insulators. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3074783]
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  • Effects of hydrogen impurities on MnxSi(1-x) semiconductors

    Wang, X. L.   Ni, M. Y.   Zeng, Z.   Lin, H. Q.  

    In the present work, we have chosen different configurations to perform relaxations to determine the ground states of hydrogen doping in Mn(x)Si(1-x), respectively. Our results show that hydrogen impurity intends to bond strongly to Mn ion in Mn(x)Si(1-x). After introducing hydrogen, the phase transfer occurs from a half metallic one to a metallic case, and the magnetic moment of Mn ion is reduced. In Mn(x)Si(1-x), Mn ions exhibit a strong short-range antiferromagnetic and long-range ferromagnetic interaction. However, with the hydrogen doping, the exchange interactions of Mn ions oscillate between antiferromagnetic coupling and ferromagnetic coupling as a function of the distances between Mn ions. Hydrogen significantly influences the properties of Mn(x)Si(1-x). (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3072081]
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  • Effects of hydrogen impurities on Ge(1-x)Mn(x) semiconductors

    Wang, X. L.   Ni, M. Y.   Zeng, Z.   Lin, H. Q.  

    The structural and magnetic properties of hydrogen-doped Ge(1-x)Mn(x) diluted magnetic semiconductors are investigated using a first-principles pseudopotential method. Our results show that hydrogen impurities intend to bond to Mn ions in the Mn-doped Ge system and strongly influence the magnetic properties of this system. Hydrogen impurities actually reduce the Curie temperature of this system and might be one of the reasons for the existence of paramagnetic samples of Ge(1-x)Mn(x). Alternatively, hydrogenation can provide an easy and nonvolatile way to control and pattern the ferromagnetic properties of Mn-doped Ge diluted magnetic semiconductors, which has been achieved in the Mn-doped GaAs system (GOENNENWEIN S. T. B. et al., Phys. Rev. Lett., 92 (2004) 227202). Copyright (C) EPLA, 2009
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  • KAgF(3): Quasi-one-dimensional magnetism in three-dimensional magnetic ion sublattice

    Zhang, Xiaoli   Zhang, Guoren   Jia, Ting   Guo, Ying   Zeng, Zhi   Lin, H. Q.  

    The electronic structure and magnetic properties of the Jahn-Teller-distorted perovskite KAgF(3) have been investigated using the full-potential linearized augmented plane-wave method. It is found that KAgF(3) exhibits significant quasi-one-dimensional antiferromagnetism with the ratio of exchange constant vertical bar J perpendicular to vertical bar (perpendicular to the z-axis) and J (along the z-axis) about 0.04, although the sublattice of magnetic ion is three-dimensional. The strong quasi-one-dimensional antiferromagnetism originates from the C-antiferro-distortive orbital ordering of the Ag(2+) 4d(9) ions. The orbital ordered antiferromagnetic insulating state in KAgF(3) is determined by on-site Coulomb repulsion to a large extent. (C) 2011 Elsevier By. All rights reserved.
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  • Manipulating classical waves with an analogue of quantum interference in a V-type atom

    Tan, W.   Yang, C. Z.   Liu, H. S.   Wang, Z. G.   Lin, H. Q.   Chen, H.  

    We demonstrate a waveguide system containing two side-coupled resonators to explore the interference effects between two low-Q resonators. The structure closely mimics the quantum interference between two direct excitation pathways in a three-level V-type atom. We show that high-Q transparency peak can be achieved by using two low-Q resonators, and the transmission lineshape can be tuned between an EIT-like resonant peak and a Lorentzian-like resonant dip. Acoustic experiments, in good agreement with the theoretical predictions, are performed to confirm this idea. Copyright (C) EPLA, 2012
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  • The strong quasi-one-dimensional antiferromagnetism in a charge-transfer insulator: AgSO4

    Zhang, Xiaoli   Jia, Ting   Liu, Ting   Zeng, Zhi   Lin, H. Q.  

    The strong quasi-one-dimensional antiferromagnetism and the electronic structure of AgSO4 are investigated by performing the first-principles density functional calculations. The results show that the strong quasi-one-dimensional antiferromagnetic coupling in AgSO4 is along [1<(1over bar>1] diagonal of the unit cell. The superexchange interaction between the Ag1 4d(x12-y12) and the Ag2 4d(x22-22) orbitals gives rise to the unusual strong quasi-one-dimensional antiferromagnetic behavior. We also found that AgSO4 is a charge-transfer insulator. (C) 2012 American Institute of Physics. [doi:10.1063/1.3677796]
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  • Expression of globular form acetylcholinesterase is not altered in P2Y1R knock-out mouse brain

    Cui, Jane D.   Xu, Miranda L.   Liu, Etta Y. L.   Dong, Tina T. X.   Lin, H. Q.   Tsim, Karl W. K.   Bi, Cathy W. C.  

    Adenosine 5'-triphosphate (ATP), a neurotransmitter and a neuromodulator, has been shown to be co-stored and co-released with acetylcholine (ACh) at the pre-synaptic vesicles in vertebrate neuromuscular junction (nmj). Several lines of studies demonstrated that binding of ATP to its corresponding P2Y(1) receptors (P2Y(1)R) in muscle and neuron regulated the post-synaptic gene expressions. Indeed, the expression of acetylcholinesterase (AChE) in muscle was markedly decreased in P2Y1R (-/-) (P2Y(1)R knockout) mice. In order to search for possible role of P2Y(1)R in cholinergic function of the brain, the expression of globular form AChE was determined in the brain of P2Y1R (-/-) mice. In contrast to that in muscle, the amounts of AChE activity, AChE catalytic subunit, structure subunit PRiMA and the amount of ACh, in the brain were not, significantly, altered, suggesting the role of P2Y(1)R in neuron could have different function as that in muscle. However, the expressions of a series of neuronal development markers, i.e. neuro-filaments, were reduced in P2Y1R (-/-) mouse brain, indicating P2Y(1)R may be involved in neuronal development process. (C) 2016 Elsevier Ireland Ltd. All rights reserved.
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  • Pressure-induced spin-state and insulator-metal transitions in Sr3Fe2O5 from first principles

    Jia, Ting   Wu, Hua   Zhang, Xiaoli   Liu, Ting   Zeng, Zhi   Lin, H. Q.  

    Using hybrid functional calculations, we find that under the experimental pressure of 36.7 GPa, layered Sr3Fe2O5 undergoes a spin-state transition (SST) from high spin to intermediate spin. This transition is triggered by an electron depletion of the highest crystal-field level x(2) - y(2). On the other hand, a reduced inter-layer distance lifts up the antibonding 3z(2) - r(2) state, and thus its electron occupation is partially shifted to the otherwise unoccupied x(2) - y(2) conduction band. This gives rise to an insulator-metal transition (IMT). We note that the IMT is closely related to the SST, but they somewhat have a different origin. Copyright (c) EPLA, 2013
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  • Exactly soluble quantum spin models on a double layer:??The net spin model

    Lin, H. Q.   Shen, J. L.   Shik, H. Y.  

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