Structural and magnetic studies of Fe/W metallic superlattices (abstract)

We have sputter deposited Fe/W superlattices on several types of substrates using magnetically enhanced dc sputtering guns. The deposition rates were controlled to better than 0.3%. We used a 6‐MV Rutherford backscattering facility to determine the chemical composition with 0.5% relative uncertainty. We varied the modulation wavelength from Λ=4.4 to 250 Å, keeping the number of atomic layers equal for both materials. Structural characterization was achieved by several x‐ray diffraction techniques. We found that the superlattice structural coherency breaks down below Λ_c=21.5 Å, although the multilayered structural periodicity still holds below this value. We used conversion electron Mössbauer spectroscopy to measure the intrinsic hyperfine magnetic field of the samples at room temperature. The data was fitted with two independent methods which show very good agreement. We observed a decrease in the hyperfine field value as the modulation wavelength Λ decreases, and a disappearance for Λ<Λ_c. This effect is interpreted as due to structural strains of the whole superlattice and electronic structure changes at the interfaces.