Anomalous behavior of the negative magnetoresistivity in Au-Fe alloys

The magnetoresistivity of dilute Au-Fe alloys containing 0.1 at.% to 1 at.%Fe has been measured in the temperature range 2°to 77°K and in magnetic fields up to 200 kOe. Although the residual resistivity ρ is proportional to the Fe concentration, the negative magnetoresistivity Δρm/ρ, due to the freezing out of the contribution of the exchange scattering, drops rapidly with increasing Fe concentration. We find Δρm/ρ = - (A + Bc)-1, where c is the Fe concentration in at. % and A and B are parameters which depend on temperature and magnetic field. At low temperatures A and B are positive and of comparable magnitude; B is decreasing with both increasing field and increasing temperature. Above 22°K, B is small and negative. At low temperatures, two anomalies of the magnetoresistivity are observed: First, in the highest fields applied no saturation of Δρm is obtained and second, below a certain temperature T0, Δρm is no longer a function of μH/kT only, as theoretically expected [except for very slowly varying terms of the form ln (EF/μH)]. These anomalies become more pronounced with increasing impurity concentration. T0 increases from 10°K for 0.1 at.%Fe to about 50°K for 1.01 at.%Fe. By extrapolating Δρm/ρ to zero Fe concentration these anomalies remain. Therefore, they seem to be intrinsic and are merely enhanced by correlation effects between the impurities. Further, from the temperature dependence of the zero-field resistivity and the high field resistivity, the s-d interaction parameter, J, was obtained to be 0.064 eV < J < 0.1 eV. This value of J is considerably smaller than previously reported for similar alloy systems like Cu-Mn, Y-Ce and others. It is shown that the reason for such high values of J is an incorrect application of Kondo's expression for the exchange resistivity. © 1967 The American Institute of Physics.