The Effect of Pressure onFe57Hyperfine Fields in FerromagneticPdCoAlloys

The ${\mathrm{Fe}}^{57}$ hyperfine fields in a series of ferromagnetic $\mathrm{Pd}\mathrm{Co}$ alloys having cobalt concentrations between 5 and 15 at.% are measured by Mössbauer spectroscopy at 297°K and pressures up to 180 kbar. The pressure-dependent finite-temperature impurity hyperfine-field problem is parametrized in terms of the pressure dependence of the host Curie temperature, the zero-temperature hyperfine field, and the host-impurity coupling constant. In conjunction with previous data of Holzapfel et al. on the pressure dependence of the Curie temperatures, the present data are fitted within the molecular-field approximation with a positively pressure-dependent zero-temperature hyperfine field and a negatively pressure-dependent host-impurity coupling constant, the pressure derivatives being roughly composition independent. Implications of these results are discussed, and a comparison is made with the high-pressure Mössbauer data of Möller and Drickamer on $\mathrm{Pd}\mathrm{Fe}$ alloys in the same composition range. Isomer-shift data are also presented briefly.