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Large Magnetic Anisotropy of a Single Atomic Spin Embedded in a Surface Molecular Network

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Science  31 Aug 2007:
Vol. 317, Issue 5842, pp. 1199-1203
DOI: 10.1126/science.1146110
  • Fig. 1.

    Fe atoms on CuN. (A) (Left) Processed (37) constant-current topograph (10 mV, 0.5 nA) of two adjacent CuN islands with a single adsorbed Fe atom. The topograph is negative-curvature (high-pass) filtered to enhance contrast, with lattice positions of Cu (yellow dots) and N (green dots) atoms overlayed. The light vertical features on the left side of the image are formed by the absence of single rows of N atoms from the CuN surface. The topographic peak of the Fe atom (blue cross) shows its binding site: on top of a Cu site with two N atoms as horizontal neighbors. (Right) Cross section of the unfiltered topograph along the dashed line indicated in the left panel. (B) The charge density for a CuN surface on Cu(100) calculated with the DFT methods described in the text along the N (left) and hollow (right) directions. The scale for the magnitude of the charge density is shown at the bottom in units of e/a03. Solid yellow and green circles with gray edges label the centers of the Cu and N atoms, respectively. The numbers inside the circles indicate the net charge on selected atoms in units of e (25). (C) Same as (B) with an Fe atom (blue) adsorbed on the CuN on top of a surface Cu site.

  • Fig. 2.

    Conductance spectra of Fe atoms on CuN. (A) Spectra taken with the STM tip positioned above an Fe atom at T = 0.5 K and B = 0 to 7 T oriented in the N direction. The spectra were acquired at a nominal junction impedance of 10 megohm (10 mV, 1 nA) and were not sensitive to junction impedance. Successive spectra are vertically offset by 0.023 nA/mV for clarity. Red, green, and blue upward arrows indicate the positions of the first, second, and third excitations, respectively, at B = 0 T as calculated by Eq. 1 with the fit parameters described in the text. Downward arrows show the same excitations at B = 7 T with the magnetic field oriented along the z axis of Eq. 1. (B) Same as (A) with B oriented along the hollow direction for the spectra; this direction corresponds to the x axis of Eq. 1. Also included are magenta downward arrows indicating the calculated position of the fourth transition at B = 7 T. (C) Energies for the first (red triangles), second (green circles), and third (blue triangles) steps observed in the spectra acquired with B along the N direction, including those shown in (A). Solid lines indicate excitation energies calculated by Eq. 1 with the magnetic field oriented along the z axis. (D) Step energies for the spectra acquired with B along the hollow direction, which corresponds to the x axis of Eq. 1, including those shown in (B). (E) Relative step heights for the first (red), second (green), and third (blue) excitations as a function of B along the N direction. The individual step heights are normalized by the sum of the three step heights at each value of B. The fourth excitation is not included because its intensities are negligible in this range of B. Solid lines denote normalized transition intensities calculated using Eq. 2 with the fit parameters discussed in the text. (F) Simulated spectra, as described in the text, with B along the hollow direction and an effective temperature of 0.8 K. Arrows are the same as in (B). These spectra are scaled by an overall constant and offset to match those shown in (B). a.u., arbitrary units.

  • Fig. 3.

    Conductance spectra and structure of Mn atoms on CuN. (A) Spectra (black) taken with the tip positioned above a Mn atom at T = 0.5 K, with the magnetic field oriented out-of-plane. All spectra were acquired at a nominal junction impedance of 10 megohm (10 mV, 1 nA) andare offset by 0.025 nA/mV for clarity. Red lines represent simulated spectra with an effective temperature of 0.7 K. The simulated inelastic spectra are scaled by an overall constant and offset to match the observed spectra. (B) Step energy of two different Mn atoms, indicated by circles and triangles, with B oriented out-of-plane. Colored lines show the possible transitions energies calculated using Eq. 1 with the fit parameters listed in the text for B along the z direction. Because the anisotropy parameters are substantially smaller than those for Fe, level crossings complicate the assignment of the spin excitations at small magnetic fields. (C) Charge density for a Mn atom adsorbed on a CuN surface on Cu(100) calculated by DFT along the N and hollow directions. Solid yellow, green, and blue circles with gray edges label the centers of the Cu, N, and Mn atoms, respectively. The charge-density scale is the same as that shown in Fig. 1.

  • Fig. 4.

    Calculated net–spin-density distribution for Fe on CuN. Contours (purple) of constant net spin density (0.01 e/a 30), as calculated by DFT for an Fe atom adsorbed on a Cu site on a CuN surface, are shown (25). Only the Fe atom and the atoms in the CuN surface layer are shown for clarity. Small yellow, green, and blue balls indicate the positions of the Cu, N, and Fe atoms, respectively, in the surface layer.

  • Table 1.

    Eigenvectors of the spin Hamiltonian for Fe on CuN. A list of eigenvectors, written as a sum of lm〉 states and obtained by diagonalizing Eq. 1 with S = 2, g = 2.11, D = -1.55 meV, and E = 0.31 meV at B = 0 T and at B = 7 T oriented along the N direction is shown.

    Eigenstate|+2〉|+1〉|+0〉|-1〉|-2〉
    B = 0 T
    ψ0 0.697 0 -0.166 0 0.697
    ψ1 0.707 0 0 0 -0.707
    ψ2 0 0.707 0 -0.707 0
    ψ3 0 0.707 0 0.707 0
    ψ4 0.117 0 0.986 0 0.117
    B = 7 T
    ψ0 0.021 0 -0.097 0 0.995
    ψ1 0.987 0 -0.157 0 -0.036
    ψ2 0 0.402 0 -0.916 0
    ψ3 0 0.916 0 0.402 0
    ψ4 0.159 0 0.983 0 0.092

Additional Files


  • Large Magnetic Anisotropy of a Single Atomic Spin Embedded in a Surface Molecular Network
    Cyrus F. Hirjibehedin, Chiung-Yuan Lin, Alexander F. Otte, Markus Ternes, Christopher P. Lutz, Barbara A. Jones, Andreas J. Heinrich

    Supporting Online Material

    This supplement contains:
    Figs. S1 and S2

    Correction (28 September 2007):
    The legends to Figures S1 and S2 were omitted from the original SOM. They appear correctly here. The original version can be found here

    This file is in Adobe Acrobat PDF format.

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