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  • 1.
    Engström, Christian
    Lund University, Sweden.
    Structural information of nanocomposites from measured optical properties2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 10, article id 106212Article in journal (Refereed)
    Abstract [en]

    This paper is concerned with the estimation of the volume fraction and the anisotropy of a two-component composite from measured bulk properties. An algorithm that takes into account that measurements have errors is developed. This algorithm is used to study data from experimental measurements for a nanocomposite with an unknown nanostructure. The dependence on the nanostructure is quantified in terms of a measure in the representation formula introduced by D Bergman. We use composites with known nanostructures to illustrate the dependence on the underlying measure and show how errors in the measurements affect the estimates of the structural parameters.

  • 2.
    Gryglas-Borysiewicz, Marta
    et al.
    University of Warsaw, Poland.
    Juszynski, Piotr
    University of Warsaw, Poland.
    Kwiatkowski, Adam
    University of Warsaw, Poland.
    Przybytek, Jacek
    University of Warsaw, Poland.
    Sadowski, Janusz
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Lund University ; Polish Academy of Sciences, Poland.
    Sawicki, Maciej
    Polish Academy of Sciences, Poland.
    Tokarczyk, Mateusz
    University of Warsaw, Poland.
    Kowalski, Grzegorz
    University of Warsaw, Poland.
    Dietl, Tomasz
    Polish Academy of Sciences, Poland ; University of Warsaw, Poland ; Tohoku University, Japan.
    Wasik, Dariusz
    University of Warsaw, Poland.
    Hydrostatic-pressure-induced changes of magnetic anisotropy in (Ga, Mn) As thin films2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 11, article id 115805Article in journal (Refereed)
    Abstract [en]

    The impact of hydrostatic pressure on magnetic anisotropy energies in (Ga, Mn) As thin films with in-plane and out-of-plane magnetic easy axes predefined by epitaxial strain was investigated. In both types of sample we observed a clear increase in both in-plane and out-of-plane anisotropy parameters with pressure. The out-of-plane anisotropy constant is well reproduced by the mean-field p-d Zener model; however, the changes in uniaxial anisotropy are much larger than expected in the Mn-Mn dimer scenario.

  • 3.
    Gustafsson, Alexander
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Paulsson, Magnus
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    STM contrast of a CO dimer on a Cu(111) surface: a wave-function analysis2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 505301Article in journal (Refereed)
    Abstract [en]

    We present a method used to intuitively interpret the scanning tunneling microscopy (STM) contrast by investigating individual wave functions originating from the substrate and tip side. We use localized basis orbital density functional theory, and propagate the wave functions into the vacuum region at a real-space grid, including averaging over the lateral reciprocal space. Optimization by means of the method of Lagrange multipliers is implemented to perform a unitary transformation of the wave functions in the middle of the vacuum region. The method enables (i) reduction of the number of contributing tip-substrate wave function combinations used in the corresponding transmission matrix, and (ii) to bundle up wave functions with similar symmetry in the lateral plane, so that (iii) an intuitive understanding of the STM contrast can be achieved. The theory is applied to a CO dimer adsorbed on a Cu(1 1 1) surface scanned by a single-atom Cu tip, whose STM image is discussed in detail by the outlined method.

  • 4.
    Islam, Fhokrul
    et al.
    Virginia Commonwealth University, USA.
    Khanna, Shiv
    Virginia Commonwealth University, USA.
    On the enhancement of magnetic anisotropy in cobalt clusters via non-magnetic doping2014In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 125303Article in journal (Refereed)
    Abstract [en]

    We show that the magnetic anisotropy energy (MAE) in cobalt clusters can be significantlyenhanced by doping them with group IV elements. Our firstprincipleselectronic structurecalculations show that Co4C2 and Co12C4 clusters have MAEs of 25 K and 61 K, respectively. The large MAE is due to controlled mixing between Co dandC pstatesand can be furthertuned by replacing C by Si. Larger assemblies of such primitive units are shown to be stablewith MAEs exceeding 100 K in units as small as 1.2 nm, in agreement with the recentobservation of large coercivity. These results may pave the way for the use of nanoclustersinhigh density magnetic memory devices for spintronics applications

  • 5.
    Mahani, Mohammad Reza
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Pertsova, Anna
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Canali, Carlo M.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Trend of the magnetic anisotropy for individual Mn dopants near the (110) GaAs surface2014In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 39, p. Article ID: 394006-Article in journal (Refereed)
    Abstract [en]

    Using a microscopic finite-cluster tight-binding model, we investigate the trend of the magnetic anisotropy energy as a function of the cluster size for an individual Mn impurity positioned in the vicinity of the (1 1 0) GaAs surface. We present results of calculations for large cluster sizes containing approximately 104 atoms, which have not been investigated so far. Our calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs, found to be non-zero in previous tight-binding calculations, is purely a finite size effect that vanishes with inverse cluster size. In contrast to this, we find that the splitting of the three in-gap Mn acceptor energy levels converges to a finite value in the limit of the infinite cluster size. For a Mn in bulk GaAs this feature is related to the nature of the mean-field treatment of the coupling between the impurity and its nearest neighbor atoms. We also calculate the trend of the anisotropy energy in the sublayers as the Mn dopant is moved away from the surface towards the center of the cluster. Here the use of large cluster sizes allows us to position the impurity in deeper sublayers below the surface, compared to previous calculations. In particular, we show that the anisotropy energy increases up to the fifth sublayer and then decreases as the impurity is moved further away from the surface, approaching its bulk value. The present study provides important insights for experimental control and manipulation of the electronic and magnetic properties of individual Mn dopants at the semiconductor surface by means of advanced scanning tunneling microscopy techniques.

  • 6.
    Manchon, A.
    et al.
    Department of Physics, University of Arizona, Tucson, AZ 85721, USA ;SPINTEC, URA 2512 CEA/CNRS, 38054 Grenoble Cedex 9, France .
    Pertsova, Anna
    Department of Physics, M V Lomonosov Moscow State University, Leninskie Gori, 1199992 Moscow, Russia .
    Ryzhanova, N.
    SPINTEC, URA 2512 CEA/CNRS, 38054 Grenoble Cedex 9, France; Department of Physics, M V Lomonosov Moscow State University, Leninskie Gori, 1199992 Moscow, Russia.
    Vedyayev, A.
    SPINTEC, URA 2512 CEA/CNRS, 38054 Grenoble Cedex 9, France; Department of Physics, M V Lomonosov Moscow State University, Leninskie Gori, 1199992 Moscow, Russia .
    Dieny, B.
    SPINTEC, URA 2512 CEA/CNRS, 38054 Grenoble Cedex 9, France.
    Currents and torques due to spin-dependent diffraction in ferromagnetic/spin spiral bilayers2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 50, p. 505213-Article in journal (Refereed)
    Abstract [en]

    Spin-dependent transport through the interface between a ferromagnet and a spin spiral is investigated using both ballistic and diffusive models. We find that spin-dependent interferences lead to a new type of diffraction called 'spin diffraction'. It is shown that this spin diffraction leads to local spin and electrical current along the interface, as well as spin transfer torque acting on the spin spiral. This study also emphasizes that in highly inhomogeneous magnetic configurations, diffracted electrons must be taken into account to properly describe the spin transport.

  • 7.
    Pertsova, Anna
    et al.
    School of Physics and CRANN, Trinity College Dublin, Ireland.
    Stamenova, M.
    School of Physics and CRANN, Trinity College Dublin, Ireland.
    Sanvito, S.
    School of Physics and CRANN, Trinity College Dublin, Ireland.
    Time-dependent electron transport through a strongly correlated quantum dot: multiple-probe open-boundary conditions approach2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 10, p. 105501-Article in journal (Refereed)
    Abstract [en]

    We present a time-dependent study of electron transport through a strongly correlated quantum dot, which combines adiabatic lattice density functional theory in the Bethe ansatz local-density approximation (BALDA) to the Hubbard model, with the multiple-probe battery method for open-boundary simulations in the time domain. In agreement with the recently proposed dynamical picture of Coulomb blockade, a characteristic driven regime, defined by regular current oscillations, is demonstrated for a certain range of bias voltages. We further investigate the effects of systematically improving the approximation for the electron–electron interaction at the dot site (going from non-interacting, through Hartree-only to adiabatic BALDA) on the transmission spectrum and the IV characteristics. In particular, a negative differential conductance is obtained at large bias voltages and large Coulomb interaction strengths. This is attributed to the combined effect of the electron–electron interaction at the dot and the finite bandwidth of the electrodes.

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