Ferromagnetic and spin-glass ordering in Fe-doped auxPd1-x alloys

Ferromagnetic and spin-glass ordering has been studied in (AuxPd1-x)1-cFec alloys for 0<~x<~1 and 0<. 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 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 Tc(c) data, where Tc 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.