Magnetism in Amorphous Fe-Pd-P Alloys

Amorphous alloys of composition ${\mathrm{Fe}}_x{\mathrm{Pd}}_{80-x}{\mathrm{P}}_{20}$ ($13\le x\le 44$) have been prepared by rapid quenching from the liquid state. The Mössbauer effect in ${\mathrm{Fe}}^{57}$ has been used to study the magnetic properties of these materials. The hyperfine field distribution has been determined from these experiments, as a function of composition and temperature. The results indicate that the electronic state of Fe in these alloys remains essentially constant throughout the composition range, and that the Pd $d$ band is filled by electron transfer from phosphorus. The variation of the magnetic transition temperature with composition has been determined by combining the Mössbauer-effect results with complementary magnetic measurements. There is a sharp change in slope in this curve at $x\simeq 26$. Below this concentration, the long-range magnetic order which prevails in the higher-Fe-concentration alloys breaks down, giving rise to a more local ordering. The Mössbauer-effect results confirm the existence of weakly coupled Fe atoms in all the amorphous Fe-Pd-P alloys. These atoms reside in low effective fields, and can participate in the spin-flip-scattering process which produces a Kondo effect (resistivity minimum). The large critical concentration observed is also an indication that the spin correlations are greatly reduced in these amorphous alloys.