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@INPROCEEDINGS{Jourdan:207369,
      author       = {Jourdan, M. and Minár, J. and Braun, J. and Kronenberg, A.
                      and Chadov, S. and Balke, B. and Gloskovskii, A. and Kolbe,
                      M. and Elmers, H. J. and Schönhense, G. and Ebert, H. and
                      Felser, C. and Kläui, M.},
      title        = {{T}he {Q}uest for and {D}emonstration of direct
                      {E}xperimental {E}vidence for half {M}etallicity in
                      {H}eusler {C}ompounds},
      reportid     = {PUBDB-2015-01317},
      year         = {2014},
      abstract     = {Spin transport electronics (spintronics) is commonly
                      considered as a promising future information technology,
                      which motivates the search for new materials for optimum
                      device performance. The key parameter for the magnitude of
                      spin transport effects is the spin polarization, which
                      ideally amounts to $100\%$ in so-called half-metals.
                      However, clear room temperature evidence for this property
                      has been reported so far only for some oxides, which are not
                      suitable for the incorporation into electronic devices. On
                      the other hand, for Heusler compounds half-metallicity was
                      predicted theoretically already more than ten years ago
                      (e.g. [Gal02]), but direct experimental evidence for an
                      exceptionally high spin polarization, especially at room
                      temperature, has proven elusive and no reports exist up to
                      now. In tunneling juctions with spin-filtering epitaxial MgO
                      barriers Heusler electrodes show large magnetoresistance
                      effects (e.g. [Liu12]), but still are inferior to
                      conventional CoFeB electrodes (e.g. [Ick08]).Our exclusion
                      of possible extrinsic effects which reduce the
                      experimentally determinable spin polarization started with
                      the optimization of growth conditions of epitaxial Heusler
                      thin films, which we first used as electrodes of tunneling
                      magnetoresistance (TMR) junctions with AlOx barrier. It
                      could be demonstrated, that the barrier properties are
                      crucial and probably limiting the obtainable TMR values
                      [Her09]. However, x-ray magnetic circular dichroism (XMCD)
                      experiments indicated a high spin polarization of the
                      Heusler thin films [Kal09]. Thus we developed a new
                      experimental set-up, which allows for the in-situ
                      investigation of epitaxial Heusler thin films by highly
                      efficient spin-polarized photoemission spectroscopy [Kol11].
                      After a systematic study of the suitability of several
                      compounds [Jou11] this approach soon produced a record value
                      at that time of the directly observed spin-polarization of
                      $55\%$ at room temperature for the compound Co2MnGa
                      [Kol12].The breakthrough was achieved very recently [Jou14]:
                      For the first time half-metallicity at room temperature was
                      demonstrated for a Heusler compound. Investigating thin
                      films of the compound Co2MnSi deposited in optimized growth
                      conditions by in-situ spin-resolved UV-photoemission
                      spectroscopy, it was possible to reveal the high spin
                      polarization: In the surface region of Heusler thin films
                      (93+7−11) $\%$ spin polarization at room temperature was
                      measured directly. This experimental result is in excellent
                      agreement with theoretical computations of the electronic
                      properties of the investigated compound, which include
                      surface effects in a novel way. Ex-situ spin-integrated high
                      energy x-ray photoemission spectroscopy (HAXPES) experiments
                      on capped Co2MnSi thin films were explained by the same band
                      structure and photoemission calculation including all
                      surface related effects. It shows that the observation of a
                      high spin polarization in a wide energy range below the
                      Fermi energy is related to a stable surface resonance in the
                      majority band of Co2MnSi extending deep into the bulk of the
                      material.Our results show that careful thin film preparation
                      can indeed result in a high spin polarization with a
                      sufficient degree of stability in a surface region of
                      several atomic layers. In particular they demonstrate that
                      the observed room temperature tunneling magnetoresistance
                      values are not limited by the intrinsic spin polarization of
                      the Heusler alloy and that potentially much larger TMR
                      values can be obtained by carefully optimized device
                      preparation.References: [Gal02] Galanakis, I., Dederichs, P.
                      H. $\&$ Papanikolaou, Phys. Rev. B 66, 174429 (2002).[Liu12]
                      Liu, H. et al. Appl. Phys. Lett. 101,132418 (2012).[Ick08]
                      Ikeda, S. et al. Appl. Phys. Lett. 93,082508 (2008).[Her09]
                      Herbort, C., Arbelo Jorge, E. $\&$ Jourdan, M. Appl. Phys.
                      Lett. 94, 142504 (2009).[Kal09] Kallmayer, M. et al. Phys.
                      Rev. B 80, 020406 (2009).[Kol11] Kolbe, M. et al. Phys. Rev.
                      Lett. 107,207601 (2011).[Jou11] Jourdan, M. et al. J. Phys.
                      D: Appl. Phys. 44, 155001 (2011).[Kol12] Kolbe, M. et al.
                      Phys. Rev. B 86, 024422 (2012).[Jou14] Jourdan, M. et al.
                      Nat. Commun. 5, 3974},
      month         = {Nov},
      date          = {2014-11-03},
      organization  = {59th Magnetism $\&$ Magnetic Materials
                       Conference (2014), Honolulu (USA), 3
                       Nov 2014 - 7 Nov 2014},
      subtyp        = {Invited},
      cin          = {DOOR / FS-PEX},
      ddc          = {500},
      cid          = {I:(DE-H253)HAS-User-20120731 / I:(DE-H253)FS-PEX-20130206},
      pnm          = {PETRA Beamline P03 (POF2-54G14)},
      pid          = {G:(DE-H253)POF2-P03-20130405},
      experiment   = {EXP:(DE-H253)P-P03-20150101},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://bib-pubdb1.desy.de/record/207369},
}