Structural and Transport Properties of Cobalt/rhenium and Cobalt/titanium Multilayer Films.

Equal-thickness Co/Re and Co/Ti multilayer films with periods 14-220 A and Co/Re superlattices with structures Si/Re50A (Co20A/RexA) _{40} (x_{rm Re} = 3-32 A) have been prepared on glass and oxidized Si substrates (at {~}40^circC) by using a modified single-source RF triode sputtering systems. Preliminary sample characterizations including total film thickness, average film composition and oxidation of constituents have been performed using step profiler, electron microprobe and x-ray photoelectron measurements, respectively. The structural properties of these multilayered films have been investigated in detail by low- and high -angle x-ray diffraction measurements (including both theta-2theta scan and rocking curves). The structures of several Co/Ti samples have also been investigated by cross-sectional high resolution transmission electron microscopy. An optical model which includes both interfacial mixing profiles and layer-thickness disorders has been developed along with the footprint corrections and the fitting procedure for the analysis of low-angle x-ray reflectivity data. High-angle diffraction data of the Co/Re superlattices have been analysed using a trapezoidal model which considers crystalline multilayer films having extended interfaces with a linear composition profile. For the sake of comparison, high-angle diffraction spectra of pure Co, Re and Ti films and the x-ray reflectivity data of Co/Re bilayers films are also presented. Magnetic properties have been studied on the series of films with structures Si(oxidized)/Re50A (Co20A/RexA) _{40} (x_ {rm Re} = 3-32 A) in order to investigate the giant magnetoresistance (MR) effect and the oscillatory interlayer magnetic coupling. The MR has been measured at temperatures between 4.2 and 300 K for three configurations of the magnetic field (up to 1 Tesla): (i) in the film plane and perpendicular to the current direction (transverse MR (TMR)), (ii) in the film plane and paralleled to the current direction (longitudinal MR (LMR)), and (iii) perpendicular to the film plane (perpendicular MR (PMR)). Both TMR and LMR exhibit oscillatory behavior as a function of Re layer thickness with a period of {~eq}12 A and a maximum transverse MR of { ~eq}1.2% for x_ {rm Re} = 5 A at 4.2 K. The MR of the antiferromagnetically coupled samples has been analysed by using a semiclassical model; the temperature dependence of the MR has also been analysed phenomenologically. In order to study the importance of interfacial mixing, we have investigated the effect of annealing on the structural and magnetic properties of three antiferromagnetically coupled samples (x_{rm Re} = 3, 5, and 7 A) and a ferromagnetically coupled one (x_{rm Re} = 10 A). The correlation between magnetic and structural properties of these films has also been presented. The resistivities of the equal-thickness Co/Re and Co/Ti multilayer films have been measured at temperatures for 77 to 300 K. The comparison of the transport properties (resistivity and temperature coefficient of resistivity) between Co/Re and Co/Ti multilayer systems in relationship to their different structural properties has been outlined.