Magnetic and transport properties of Fe-Au and Co-Au films

Thin film cobalt-gold and iron-gold alloys have been prepared by sputtering onto water cooled substrates. These alloys are crystalline with residual electrical resistivity (ρ) a factor of five greater than bulk alloys. For FexAu100-x the X-ray diffraction patterns are characteristic of fcc structures (high Au content) and bcc structures (low Au content); CoxAu100-x shows mixed fcc and hexagonal diffraction patterns. Fe-Au exhibits a constant magnetic moment per Fe of μB = 2.2 over the range 26 to 92% Fe. The resistivity of Fe-Au at 4.2°K is about 40μΩcm and is independent of composition. The Hall effect expressed as Rs/ρ2 where Rs is the spontaneous Hall coefficient increases with Fe dilution. Co-Au shows a concentration dependent magnetic moment which decreases with increasing Au and a Hall effect as given by Rs/ρ2 which increases in magnitude as the Co moment decreases. In addition the resistivity at 4.2°K of Co-Au is composition dependent increasing with decreasing Co content. The anisotropic magneto-resistance in both Fe-Au and Co-Au behave similarly with the interesting feature that Δρ(Δρ = ρ∥- ρ⊥) has a maximum at about the same average magnetization as found for other alloys such as Ni-Fe and Ni-Co2. At the same composition of maximum Δρ the saturation magnetostriction becomes almost zero.