% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@INPROCEEDINGS{Ptter:844524,
      author       = {Pütter, Sabine and Syed Mohd, Amir and Mattauch, Stefan
                      and Koutsioumpas, Alexandros and Brückel, Thomas},
      title        = {{P}olarized neutron investigation of ultrathin {C}o films
                      on polycrystalline {P}t under {UHV}},
      reportid     = {FZJ-2018-01934},
      year         = {2017},
      abstract     = {Ultrathin magnetic films have been studied for a long time
                      [1,2] but they are still in focus since in spintronics the
                      electron spin has emerged as an additional degree of
                      freedom, besides the electron charge [3]. Crucial for
                      spintronics is the quality of the interface between the
                      substrate and the film or within heterostructures, e.g.[4].
                      Apparently, ultra high vacuum (UHV) conditions are required
                      for the study of their properties, as e.g. the magnetic
                      interface anisotropy changes on thin film contamination with
                      adsorbats [5] or on covering the thin film with protecting
                      cap layers [6,7]. For this reason, in-situ experiments are
                      preferable. A straightforward way to determine the magnetic
                      moment of thin films and to study them with depth resolution
                      is polarized neutron reflectometry (PNR) [8]. However, PNR
                      measurements of thin magnetic films under UHV conditions
                      have not yet been performed, to our knowledge. The reason is
                      that a UHV growth chamber occupies a lot of space which is
                      generally limited at beam lines.In order to solve that
                      problem, we have designed a small UHV chamber which is on
                      one hand capable of transferring a sample from thin film
                      fabrication at an MBE system to a neutron reflectometer and
                      on the other hand can be used as measurement chamber for PNR
                      [9]. It consists of a DN CF-40 cube with two opposing
                      sapphire windows for the neutron beam, a combined non
                      evaporable getter and ion pump for keeping the vacuum, a
                      wobble stick, which is needed for in-situ sample transfer
                      and also serves as sample holder for samples of up to 1
                      $cm^2$ and a valve for mounting the chamber to the MBE
                      system and exchanging samples. The pressure in the transfer
                      chamber is kept in the 10e−10 mbar range during transport
                      and PNR measurement. The length of chamber is about 30 cm
                      plus 50 cm translation length of the wobble stick and weighs
                      about 10 kg.The magnetic neutron reflectometer with high
                      incident angle (MARIA) at the Heinz Maier-Leibnitz Zentrum
                      (MLZ) in Garching, Germany is a dedicated instrument for
                      polarized neutron reflectometry of thin films [10]. In an
                      adjacent building thin films can be fabricated with an MBE
                      setup.Our UHV transport chamber was specially designed to
                      fit into the magnet of MARIA and to be attached to the MBE
                      setup. We present PNR measurements on polycrystalline Co
                      thin films of different thickness which were grown in the
                      MBE setup on 20 nm Pt/MgO(100) and measured afterwards at
                      MARIA in a magnetic field of 300 mT at room temperature,
                      under UHV conditions and at ambient air. Our experiments
                      evidence that the UHV chamber works properly and proof that
                      measurements in UHV are crucial.First of all, PNR
                      investigations of a 30 Å Co film were performed in UHV.
                      Afterwards the sample was taken out of the UHV chamber and
                      was exposed to ambient air for 6 hours before measuring it
                      with PNR again. Data treatment was performed with the
                      program GenX [11].The measurements in UHV do not give any
                      hint on oxidation of the Co film. In contrast, the
                      corresponding PNR curves of the ex-situ measured Co film
                      differ clearly from the ones measured in UHV. As a result,
                      the 30 Å Co film has transformed to 9 Å $CoO_x$ film with
                      26 Å Co beneath in the six hours. To summarize, we evidence
                      that the UHV chamber works properly which means samples
                      which are delicate to handle in ambient conditions can be
                      measured using our small UHV chamber. Second, we will
                      discuss the issue of reduced magnetic moments at interfaces,
                      which is also called „magnetic dead layers“. It is well
                      known, that the magnetic moment of thin films is reduced at
                      the interface between thin film and the substrate [12,13].
                      With our measurements we proof that the magnetic moment of
                      Co films is reduced at each interface, also at a Pt cap
                      layer. In literature, however, cap layers are only discussed
                      in terms of the change of the perpendicular magnetic
                      anisotropy [6,7], which is obviously only part of the
                      story.As third point, we study by PNR how the magnetic
                      moment changes for thin films with thickness. We performed
                      PNR measurements under UHV conditions for Co film of
                      thickness 1.5 nm, 2 nm, 3 nm and 6 nm. We observe that there
                      is a magnetic gradient in the Co film up to 3 nm.
                      Nevertheless, the average magnetic moment in Co film is
                      increasing with its thickness and tends to be bulk value at
                      6 nm. Access to PNR measurements at MARIA, sample
                      preparation with the MBE system and the usage of the
                      transport chamber for measuring is provided to all people
                      interested via the MLZ user office system (www.mlz-garching)
                      and the nanoscience foundry and fine analysis project (NFFA,
                      www.nffa.eu) where you can also apply for funding.This
                      project has received funding from the EU’s H2020 research
                      and innovation programme under grant agreement n.},
      month         = {Apr},
      date          = {2017-04-24},
      organization  = {Intermag Europe 2017, Dublin
                       (Ireland), 24 Apr 2017 - 28 Apr 2017},
      subtyp        = {After Call},
      cin          = {JCNS (München) ; Jülich Centre for Neutron Science JCNS
                      (München) ; JCNS-FRM-II / JCNS-2},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-2-20110106},
      pnm          = {524 - Controlling Collective States (POF3-524) / 6212 -
                      Quantum Condensed Matter: Magnetism, Superconductivity
                      (POF3-621) / 6G15 - FRM II / MLZ (POF3-6G15) / 6G4 - Jülich
                      Centre for Neutron Research (JCNS) (POF3-623)},
      pid          = {G:(DE-HGF)POF3-524 / G:(DE-HGF)POF3-6212 /
                      G:(DE-HGF)POF3-6G15 / G:(DE-HGF)POF3-6G4},
      experiment   = {EXP:(DE-MLZ)MBE-MLZ-20151210 / EXP:(DE-MLZ)MARIA-20140101},
      typ          = {PUB:(DE-HGF)24},
      url          = {https://juser.fz-juelich.de/record/844524},
}