Experimental Investigation on Exchange Interaction in Platinum-Iron Alloys

Abstract

Measurements of the temperature dependence of the hyperfine magnetic field $H_i$ at Fe nuclei and the concentration dependence of the transition temperature $T_c$ in platinum-iron alloys have been carried out by using the Mössbauer-effect technique. These experiments have been done in a series of dilute alloys ranging between 1 and 15 at.% of iron concentration. We find that at low temperatures ($T\ll T_c$), $H_i$ is nearly the same at each Fe nucleus. As the temperature is increased, a broadening of the absorption lines of the Mössbauer spectra is observed. Such broadening may be due to the presence of a rather wide distribution of fields $H_i$, although relaxation effects cannot be completely ruled out. The concentration dependence of the transition temperature $T_c$ can be related to a short-range interaction (not necessarily first nearest neighbors) between magnetic atoms (for Fe concentrations between about 2 and 8 at.%), and to a longer-range weaker interaction (below 1 at.% Fe) between magnetic impurities via the enhanced conduction-electron polarization of the platinum matrix.