Structural and transport properties of Fe/Ti multilayers

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Abstract
Fe/Ti metallic multilayers with an average Fe33Ti67 composition have been studied by X-ray diffraction, Mossbauer spectroscopy and electrical resistivity as a function of period. For small periods, broad diffraction peaks characteristic of a disordered, amorphous-like structure are observed, although composition modulation still exists along the growth direction. Beyond Lambda =4 nm, crystalline Ti appears with a BCC structure. It then reverts to its stable HCP form for Lambda =6 nm, with its c axis along the growth direction. At a period of 8 nm, the iron-rich layer in turn crystallises. This correlates to a sudden decrease of the electrical resistivity. The appearance of this Fe-rich BCC phase, corresponding to the onset of magnetic ordering in the Mossbauer spectra, induces a change in the texture of the titanium layer, the c axis now lying preferentially in the plane. Anomalies in both the lattice parameters and size of the crystallites occur from this period up to about 12 nm, whereas a plateau is observed for the electrical resistivity. For larger periods, the Ti content of the Fe-rich BCC phase decreases, corresponding to the further decrease of the electrical resistivity and increase of both hyperfine field and magnetic contribution in the Mossbauer spectra.