Ferromagnetism of Pd-Fe alloys produced by low-temperature ion implantation

We present low-field magnetization measurements on Pd-Fe films and foils obtained by low-temperature implantation of 175-keV ${\mathrm{Fe}}^{+}$ ions into pure Pd. dc magnetization measurements are performed in situ with a superconducting quantum-interference device magnetometer. The Curie temperatures $T_C$ of the implanted films and foils are significantly lower than the bulk values. We demonstrate that the decrease of $T_C$ is due to defects produced during implantation. Two effects are observed, an increase in the critical concentration $x_c$ for ferromagnetism and a decrease in $\frac{d{T}_C}{d{x}_{\mathrm{Fe}}}$, the rate of change of $T_C$ with the Fe concentration $x_{\mathrm{Fe}}$. Employing annealing experiments, preirradiation of Pd films and foils with ${\mathrm{Ar}}^{+}$ and ${\mathrm{He}}^{+}$ and preimplantation of ${\mathrm{O}}^{+}$, we demonstrate that changes in $x_c$ are due to oxygen-stabilized defects, whereas changes in $\frac{d{T}_C}{d{x}_{\mathrm{Fe}}}$ are due to vacancies, interstitials, and small defect clusters.