The solid-state reaction in Pt(15 nm)/Fe(15 nm) and Pt(15 nm)/Ag(10 nm)/Fe(15 nm) thin films after postannealing at 593 K and 613 K for different annealing times has been studied. The structural properties of these samples were investigated by various methods including depth profiling with secondary neutral mass spectrometry, transmission electron microscopy, and X-ray diffraction. It is shown that after annealing at the above temperatures where the bulk diffusion processes are still frozen, homogeneous reaction layers of FePt and FePt with about 10 at.% Ag, respectively, have been formed. Corresponding depth profiles of the element concentrations revealed strong evidence that the formation mechanism is based on a grain boundary diffusion induced solid-state reaction in which the reaction interfaces sweep perpendicularly to the original grain boundary. Interestingly, X-ray diffraction indicated that in both thin-film systems after the solid-state reaction the ordered L1 0 FePt

FePt thin films with a thickness of 30 nm were deposited by dc magnetron sputtering at room temperature onto SiO 2 (100 nm)/Si(100) substrates. These films were post-annealed in a temperature range of 500 C to 900 C for 30 s in three different atmospheres-N 2 , Ar, and forming gas (ArþH 2 (3 vol. %)). Irrespective of the annealing atmosphere, the chemically ordered L1 0 FePt phase has formed after annealing at 500 C. Higher annealing temperatures in N 2 or Ar atmosphere resulted in a strong increase in grain size and surface roughness but also in the appearance of a pronounced (001) texture in the FePt films. However, these films show the presence of iron oxide. In contrast, annealing in forming gas atmosphere suppressed the oxidation process and resulted in a reduced grain size and lower surface roughness. However, no (001)-but a strong (111)-texture was obtained after annealing at 700 C, which might be related to the reduced unit cell tetragonality and incorporation of hydrogen to the FePt lattice. Thus, this study clearly demonstrates that the oxygen/hydrogen content plays an important role in controlling the crystallographic orientation during post-annealing.

Pt/Fe and Pt/Ag/Fe layered films were deposited by DC magnetron sputtering on MgO(001), SrTiO3(001), and Al2O3(0001) single crystalline substrates at room temperature. The films were post-annealed between 623 K and 1173 K for 30 s in flowing N2 atmosphere. The onset of the L10-FePt phase formation in films deposited on MgO(001) and SrTiO3(001) substrates was observed after annealing between 773 and 873 K, while chemical L10 ordering sets in for Pt/Fe bilayers on Al2O3(0001) at lower temperatures accompanied by strong (001)-texture. It is concluded that elastic stress, arising from the difference in thermal expansion coefficients between film and substrate, promotes ordering and texture formation.

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