Ferromagnetic and spin-glass ordering in Fe-dopedAuxPd1−xalloys

Ferromagnetic and spin-glass ordering has been studied in ${\left({\mathrm{Au}}_x{\mathrm{Pd}}_{1-x}\right)}_{1-c}{\mathrm{Fe}}_c$ alloys for $0<~x<~1$ and $0<~c\lesssim 0.06$. Magnetic susceptibility, high-field magnetization, and Mössbauer measurements have been performed between liquid-helium and room temperature. For small $x$, the alloys are strongly exchange enhanced. Assuming that the local-moment-conduction-electron exchange coupling $J$ is independent of $x$, and employing the Takahashi-Shimizu-Doniach-Wohlfarth theory, we obtain $J=0.12\mathrm{}$ eV from the saturation moment versus host susceptibility data. The theory, however, fails to describe the interimpurity coupling that leads to magnetic order in the Pd-rich alloys. A simple phenomenological model, based on the ferromagnetic coupling of all the giant polarization clouds except those that are "isolated," gives qualitative agreement with the $T_c\mathrm{}\left(c\right)\mathrm{}$ data, where $T_c$ is the ordering temperature. The magnetic ordering changes from ferromagnetic to spin glass or mictomagnetic as $x$ increases beyond about 0.5. This seems to be connected with the change at this composition in the character of the electronic states at the Fermi level from $d$-like to $s$-like. The Au-rich samples are spin glasses understandable in terms of the Sherrington-Southern theory which is based on fluctuations in the exchange couplings of the Fe spins. The magnitude of this coupling was estimated in two ways, employing the theories of Sherrington-Southern and Larkin, and the results were in reasonable agreement with each other.