Electrical resistivity of<i>Au</i>Fe alloys in the spin-glass, mictomagnetic, and ferromagnetic regimes

Abstract

Measurements are presented of the electrical resistivity for a series of Au Fe alloys with concentrations between 0.5- and 22-at.% Fe, in the temperature range 0.5 - 300 K. We have called the concentration range between about 0.5- and 8-at.% Fe, the spin-glass regime. Here we find that the impurity resistivity $\ensuremath{\Delta}\ensuremath{\rho}$ has a ${T}^{\frac{3}{2}}$ dependence down to the lowest temperatures of measurement, the coefficient of this dependence decreasing very slowly with concentration. At higher temperatures, around the "freezing" temperature ${T}_{0}$ the impurity resistivity is increasing linearly with temperature, and this is followed, at much larger temperatures, by a very broad resistance maximum. We have called the concentration range above \ensuremath{\cong}10-at.% Fe, the mictomagnetic regime which is characterized by having large magnetic clusters and a sensitivity to thermal and magnetic history. Upon further increasing the concentration to the percolation limit $c\ensuremath{\gtrsim}15$ at.%, such that there is sufficient overlapping among these magnetic clusters, Au Fe gradually develops a long-range inhomogeneous ferromagnetic regime. Again we observe a ${T}^{\frac{3}{2}}$ temperature dependence throughout both of these regimes at low temperatures, but at higher temperatures the deviation away from this dependence is much more complicated than in the spin-glass regime. Further, the onset of magnetic ordering is clearly seen in $\ensuremath{\Delta}\ensuremath{\rho}$. We have also examined the temperature dependence of the derivative of the impurity resistivity $\frac{d(\ensuremath{\Delta}\ensuremath{\rho})}{\mathrm{dT}}$, and find that throughout our whole concentration range there is a well-defined maximum which correlates fairly well with ${T}_{0}$. The experimental and theoretical background of these measurements is fully discussed.