Structural evolution during deposition of epitaxial Fe/Pt(001) multilayers

Abstract

We have investigated the structure of epitaxial Fe/Pt(001) multilayers deposited by direct current magnetron sputtering. In these multilayers, the structure of the Fe layers depends on their thickness: Thick (tFe>22 Å) Fe layers are body-centered cubic (bcc), while thin (tFe<12 Å) Fe layers are face-centered cubic (fcc). Ex situ x-ray diffraction reveals that the unstrained lattice parameter of bcc Fe in epitaxial multilayers is significantly greater than that of bulk bcc Fe, possibly due to alloying with Pt. This suggests that the observed “fcc Fe” is actually an intermixed fcc Fe–Pt interfacial layer. To investigate this possibility, we have performed grazing-incidence x-ray scattering in situ during deposition of epitaxial Fe/Pt(001) multilayers. The structure of Fe(001) layers as thin as 10 Å is bcc, strained due to epitaxial mismatch with the Pt(001) underlayer. Additional Fe deposition results in relaxation of the bcc Fe lattice parameter toward its bulk value. Deposition of Pt onto a 50 Å thick bcc Fe(001) layer has little effect on the Fe, other than to increase its lattice parameter slightly. In contrast, deposition of Pt onto a 20-Å-thick bcc Fe(001) layer results in a partial transformation of the Fe to a fcc structure. We propose that this transformation is the result of intermixing of Pt into the previously deposited Fe layer, resulting in the formation of a fcc Fe-Pt alloy layer.