Magnetic and structural characterizations of copper/chromium and iron/molybdenum multilayered thin films

Several series of Cu/Cr and Fe/Mo multilayered structures (MLS) have been grown by ultrahigh-vacuum electron-beam evaporation on oxidized Si substrates. Structural characterizations by small-angle x-ray scattering (SAXS) and large-angle x-ray scattering (LAXS) have been carried out on Cu/Cr MLS. While the MLS with nominal bilayer periods as low as 28 angstrom exhibit layered structure, essentially no composition modulation is evident in 10 angstrom bilayer thickness films. For such films, up to ∼ 40% Cr is found to dissolve in bcc Cr to form a supersaturated solid solution. Magnetic, magnetotransport, and structural characterizations have been carried out on Fe/Mo MLS. For Fe(30 angstrom)/Mo(tMo angstrom) MLS in which the Mo layer thickness tMo is varied from 7 angstrom to 25 angstrom, hysteresis loop computer fits showed that the saturation field - which measures antiferromagnetic (AF) coupling strength A - oscillates. The maximum A is ∼ 0.47 ergs/cm2 for tMo = 11 angstrom, and slightly less than one oscillation has been observed. The low-temperature magnetoresistance (MR) oscillates similarly and attains a maximum of ∼ 2%. Several Fe(30 angstrom)/Mo(11 angstrom) MLS have been prepared at substrate temperatures Ts ranging from 150-475 K in order to systematically alter the structural properties. Low Ts samples have the largest change in resistivity upon magnetic saturation, although A and MR are largest for the 300 K sample. SAXS, LAXS, and high-resolution electron microscopy reveal a high degree of structural disorder. Low Ts samples degenerate into a heterogeneous alloy of small crystallites beyond ∼ 4-5 bilayers, while high Ts samples contain much larger crystallites but exhibit extreme propagating roughness beyond the first bilayer. The layering is most nearly intact for the 300 K sample