Mössbauer Study of Two Pd-Fe Alloys Containing Absorbed Hydrogen

The temperature dependence of hyperfine fields and isomer shifts in the system Pd-Fe-H (2 and 5% Fe) has been investigated by means of the ${\mathrm{Fe}}^{57}$ Mössbauer effect. We observe hyperfine fields indicating that an ordered magnetic structure exists in the $\beta$ phase at H concentrations high enough to cause filling of the $\mathrm{Pd}4d$ band (H/Pd≥0.59 for 2% Fe). The $\beta$-phase transition temperature $T_c\left(\beta \right)$ is considerably lower than the corresponding $\alpha$-phase transition temperature. For the 2%-Fe alloy, $T_c\left(\beta \right)=(3\mathrm{}\pm 1){}_{}{}^{\circ }{}_{}{}^{}\mathrm{K} \mathrm{and} \mathrm{H}\left(1.8\mathrm{}{}_{}{}^{\circ }{}_{}{}^{}\mathrm{K}\right)\approx 240$ kOe; for the 5%-Fe alloy, $T_c\left(\beta \right)=(10\mathrm{}\pm 3){}_{}{}^{\circ }{}_{}{}^{}\mathrm{K} \mathrm{and} \mathrm{H}\left(1.8\mathrm{}{}_{}{}^{\circ }{}_{}{}^{}\mathrm{K}\right)\approx 310$ kOe. The distribution of measured hyperfine fields has been correlated with the H near-neighbor configuration. Above $T_c\left(\alpha \right)$ and also below $T_c\left(\beta \right)$, we observe an isomer shift of +0.045±0.003 mm/sec in going from the $\alpha$ to the $\beta$ phase.