Nanocomposites and nanomaterials

Formation of the ordered L10 FePt phase in FePt films with an additional Au layer on and without substrates
Makushko P.V.1, Shamis M.N.1, Kotenko I.E.2, Schmidt N.Y.3,
Verbytska T.I.1, Makogon Iu.M.1
1 Department of Physics of Metals, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Prospect Peremogy 37, Kyiv 03056, Ukraine
E-mail: m.shamis-2021@kpi.ua
2 L.V. Pisarzhevskii Institute of Physical Chemistry of National Academy of Sciences of Ukraine, Prospect Nauky 31, Kyiv 03028, Ukraine
3 Institute of Physics, University of Augsburg, Universitätstrasse 1, 86135 Augsburg, Germany

FePt thin films are of high interest as a promising material for ultrahigh density magnetic recording media in data storage and HAMR application due to a high magnetocrystalline anisotropy, high values of saturation magnetization and corrosion resistance of ordered L10 FePt phase [1, 2].
In this study, the effect of an additional Au layer, which is located at different positions of the layer stack (top, intermediate, bottom), on A1 FePt→L10 FePt transformation the structural and magnetic properties of FePt-Au films annealed in-situ in Electron diffraction unit and compared to the annealings of films on the substrate in a vacuum furnace is investigated. Also, the L10 ordering process on substrate is studied by X-ray diffraction analysis and SQUID magnetometry. The phase composition and structure in off-substrate FePt - Au layer stacks were investigated in-situ by the RHEED method and then by the TEM. 
It was established that the location of the Au layer in the as-deposited film composition affects the parameters of its grain structure. Post-annealings activate the grain-boundary diffusion of Au and ordering processes that accompanied by the ordered L10 FePt phase formation. Depending on the grain size of the first deposited layer, these processes occur at different rates. The stresses caused by the difference in thermal expansion coefficients of Fe50Pt50 and Au are relaxed under the A1 FePt→L10 FePt transformation, which is accompanied by a decrease in volume of the unit cell. An increase in the Au concentration at the grain boundaries reduces the exchange interaction between them, which increases coercivity. In both compositions with smaller grains size of FePt films with an intermediate Au layer on the substrate and separated from it is observed the lowest temperature of the beginning of L10 phase formation.
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