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Interface characterization of Co2MnGe/Rh2CuSn Heusler multilayers

Ronny Knut, Peter Svedlindh, Oleg Mryasov, Klas Gunnarsson, Peter Warnicke, D. A. Arena, Matts Björck, Andrew J. C. Dennison, Anindita Sahoo, Sumanta Mukherjee, D. D. Sarma, Sari Granroth, Mihaela Gorgoi, and Olof Karis
Phys. Rev. B 88, 134407 – Published 10 October 2013
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  • INTRODUCTION
  • EXPERIMENT
  • RESULTS
  • DISCUSSION AND CONCLUSIONS
  • ACKNOWLEDGEMENTS
    • References

    Abstract

    To address the amount of disorder and interface diffusion induced by annealing, all-Heusler multilayer structures, consisting of ferromagnetic Co2MnGe and nonmagnetic Rh2CuSn layers of varying thicknesses, have been investigated by means of hard x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism. We find evidence for a 4 Å thick magnetically dead layer that, together with the identified interlayer diffusion, are likely reasons for the unexpectedly small magnetoresistance found for current-perpendicular-to-plane giant magnetoresistance devices based on this all-Heusler system. We find that diffusion begins already at comparably low temperatures between 200 and 250∘C, where Mn appears to be most prone to diffusion.

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    • Received 30 January 2013

    DOI:https://doi.org/10.1103/PhysRevB.88.134407

    ©2013 American Physical Society

    Authors & Affiliations

    Ronny Knut1, Peter Svedlindh2, Oleg Mryasov3, Klas Gunnarsson2, Peter Warnicke4, D. A. Arena4, Matts Björck1, Andrew J. C. Dennison1,5, Anindita Sahoo6,7, Sumanta Mukherjee7, D. D. Sarma1,7, Sari Granroth8, Mihaela Gorgoi9, and Olof Karis1

    • 1Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
    • 2Solid State Physics, Department of Engineering Sciences, Uppsala University, Box 534, 751 21 Uppsala, Sweden
    • 3Department of Physics and Astronomy and MINT Center, University of Alabama, Tuscaloosa, Tuscaloosa, Alabama 35487, USA
    • 4National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, USA
    • 5Institut Laue-Langevin, Grenoble 38042, France
    • 6Department of Physics, Indian Institute of Science, Bangalore-560 012, India
    • 7Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560 012, India
    • 8Department of Physics, University of Turku, Turku, Finland
    • 9Helmholtz Zentrum Berlin für Materialien und Energie GmbH, BESSY II, Berlin, Germany

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    Issue

    Vol. 88, Iss. 13 — 1 October 2013

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    Images

    • Figure 1
      Figure 1
      Photoemission of Rh 3d5/2 from sample CMG 18 Å/RCS 18 Å (hereafter denoted “thick layers”) after different annealing temperatures. There is a peak shift to higher binding energy with increasing annealing temperature. The spectrum obtained for 265∘C (red dashed-dotted line) has been deconvoluted in Fig. 2.Reuse & Permissions
    • Figure 2
      Figure 2
      Deconvoluted spectrum of the Rh 3d5/2 core level, fitted with three main peaks and a peak at the high BE shoulder, which is always 14% of the two main peaks at the lower BE side.Reuse & Permissions
    • Figure 3
      Figure 3
      Fractions of the total peak areas of the Rh 3d5/2 core level spectrum, corresponding to the three main peaks obtained by fitting as illustrated in Fig. 2, are plotted as a function of annealing temperature. Top: High coordination component; middle: medium coordination component; bottom: low coordination component. Data for the three different samples considered are identified as indicated in the legends. The dashed lines have been obtained from Monte Carlo simulations describing the variation of the high, medium, and low coordination number cases with annealing temperature. The three lattice illustrations show the Rh distribution for different annealing temperatures.Reuse & Permissions
    • Figure 4
      Figure 4
      The Cu 2p3/2 core level shift as a function of annealing temperature for three samples as indicated by the legends. The BE shifts are given relative to the position of the 2p level for the “thick layer” sample prior to annealing. Small shifts are found for samples with thick CMG layers (“thick layers” and “thick magn. layer”) already at 200∘C. We observe no chemical shift below 250∘C for the sample with the thick nonmagnetic layers, suggesting little modification below this temperature.Reuse & Permissions
    • Figure 5
      Figure 5
      Deconvoluted Mn 2p3/2 spectrum recorded for the “thick layer” sample. The spectrum can be fitted by two components, and associated satellites, for all annealing temperatures. There is both a BE shift and a large difference in the satellite intensity between the components.Reuse & Permissions
    • Figure 6
      Figure 6
      The intensity of the bulk (circles) and interface (squares) peaks, derived from fits such as those illustrated in Fig. 5, are plotted as a function of annealing temperature for the “thick layer” sample. Only the bulk component is plotted for the other samples (triangles and diamonds).Reuse & Permissions
    • Figure 7
      Figure 7
      The Co XMCD spin magnetic moment is plotted on the left scale. On the right scale we have plotted the chemical shift of the Co 2p3/2 core level. The behavior of the chemical shift and magnetic moment is very similar.Reuse & Permissions
    • Figure 8
      Figure 8
      Left: Polarized neutron reflectivity data for the 24 Å CMG/ 18 Å RCS sample with data for spin-up and spin-down polarization states, and their lines of best fit using the structural/magnetic model displayed as yellow (gray) and red (black) colors, respectively. Right: The interface roughness and magnetic moment obtained from the refinement using genx (Ref. 32). The roughness of RCS grown on CMG is very sensitive to annealing already at 100∘C.Reuse & Permissions
    • Figure 9
      Figure 9
      Estimated thickness of the magnetically dead layer for different layer thicknesses obtained from SQUID magnetometry. Circles: The thickness for the CMG layer has been kept constant at 18 Å, while the RCS layer thickness is varied between 6 and 24 Å. Solid diamonds: The RCS layer thickness is 18 Å, while the CMG thickness is varied between 12 and 24 Å. Open diamonds: As previous data, but the samples have been annealed at 250∘C. The dead layer thickness is relatively insensitive to the thickness of the layers.Reuse & Permissions
    • Figure 10
      Figure 10
      The Co spin magnetic moment for different CMG and RCS layer thicknesses before annealing. The top graph shows data for a constant CMG layer thickness of 18 Å varying the RCS layer thickness, while the lower graph shows data for a constant RCS layer thickness of 18 Å varying the CMG layer thickness. The dashed lines correspond to fits assuming a 4 Å magnetically dead layer and a Co spin magnetic moment of 1μB/Coatom for the two situations.Reuse & Permissions
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