| Multilayer thin films are of technological interest due to their optical, electrical, magnetic, and mechanical properties. In particular the layered structure in these films can lead to such effects as yield strength (hardness) enhancement and giant magnetoresistance (GMR). Such films have applications as hard coatings and magnetic field sensors, respectively. In this study we investigate the structure/property relationships for sputter-deposited multilayers which exhibit either enhanced hardness or GMR.;The hardnesses of epitaxial Fe(001)/Pt(001) and Fe(001)/Cr(001) and polycrystalline Fe/Pt multilayers were measured as a function of the bilayer period and the volume fraction of each component by nanoindentation. The hardness was enhanced by a factor of 2.2 to 2.8 times the rule of mixtures value in each system. X-ray diffraction of Fe(001)/Pt(001) multilayers allows us to rule out previous explanations for this enhancement such as coherency stresses, structural discontinuities, film stress, and misfit dislocation density. We have developed a model that explains the observed behavior in this system. For small bilayer periods the hardness is dominated by the spatially varying shear modulus in these films and is independent of bilayer period. For large bilayer periods dislocation pileups and dislocation bowing dominate, and the hardness of these films exhibits a Hall-Petch-like dependence on bilayer period. Our model accounts for the transition between these two regimes and is in good agreement with the experimental data.;We have also investigated the effect of doping the ferromagnetic layer on the spin-scattering, magnetoresistance, saturation field, and sensitivity (change in magnetoresistance per change in field) of epitaxial FeCr(001)/Cr(001) and CoCu(001)/Cu(001) multi-layers. Since the sensitivity is the figure of merit for magnetic field sensor applications, we are particularly interested in the change in this parameter with alloy content. In both of these antiferromagnetically coupled systems doping increases the sensitivity of the films, in some cases by nearly 150%. The effect of the dopants on the spin-dependent scattering and on the antiferromagnetic coupling strength is responsible for this sensitivity increase. This technique represents a simple way of improving the figure of merit for these multilayers. |
