A structure investigation of epitaxial Fe-Pt multilayers

Fe/Pt epitaxial multilayers have been studied by cross-sectional transmission electron microscopy and high-resolution transmission electron microscopy (HRTEM). The Fe/Pt multilayers were prepared by sputter deposition on MgO substrates. All samples had the (002)1,, p, plane parallel to the surface of MgO. The nominal bilayer period Lambda was varied from 2.5 to 12.1 nm. The multilayers with Lambda greater than or equal to 4.4 nm exhibited a Bain orientation relationship between fee Pt a lid the tetragonally distorted bcc Fe. Examination of the multilayers with Lambda = 12.1 nm revealed the least distorted bee Fe structure and the best-defined interface between the bee Fe and fcc Pt layers. The HRTEM images taken from the areas adjacent to the interface revealed that (200)(bccFe) is rotated 3degrees away from (200)1,,. This rotation appears to arise in order to accommodate the elastic misfit between the layers. The ratio of the interplanar distance of the (002)(bccFe) planes relative to that Of (110)(bccFe), that is d(002)(Fe)/d(110) (Fe), was found to be 1.37 for Lambda = 7.6 nin and 1.28 for Lambda = 4.4 nin, which are smaller than the value of 1.414 expected for an undistorted bee structure. The variation in the ratio could be related to a relaxation of the internal stresses developed in the multilayers. For the Fe/Pt multilayers with a nominal value of Lambda = 2.5 nm, both the selected area diffraction patterns and the HRTEM images show epitaxial growth of fcc Fe and Pt with a cube-on-cube orientation relationship, that is [010](Fe)//[010](Pt), (002)(Fe)//(002)(pt), with about 1degrees deviation. A tetragonal distortion occurred in the Pt layers with the largest lattice constant in the plane of the film. Diffuse diffraction spots and streaking along the film growth direction were observed in all multilayers, probably owing to a combination of both the small dimensions of the layer structure and the formation of a Fe/Pt solid solution close to the interfaces.