Magnetization Distribution in a Palladium-Rich FePd Alloy

Abstract

A ferromagnetic ${\mathrm{Fe}}_{0.013}$ ${\mathrm{Pd}}_{0.987}$ single crystal was examined with the polarized-beam neutron-diffraction technique in a study of the distribution of the localized magnetization in the alloy. Intensities of all nineteen Bragg reflections out to $\frac{sin\ensuremath{\theta}}{\ensuremath{\lambda}}=0.90$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$ were measured at 4.2\ifmmode^\circ\else\textdegree\fi{}K in a field of 14 kOe, yielding the magnetic form factor averaged over all atoms. These data are fitted to a linear combination of calculated $3d$ and $4d$ free-atom form factors, resulting in a moment of $0.050\ifmmode\pm\else\textpm\fi{}0.006 {\ensuremath{\mu}}_{B}$ of $3d$-like moment and $0.088\ifmmode\pm\else\textpm\fi{}0.008 {\ensuremath{\mu}}_{B}$ of $4d$-like moment per average atom. A Fourier inversion of the magnetic scattering amplitudes emphasizes the aspherical shape of the unpaired-electron distribution. The over-all $\frac{{E}_{g}}{{T}_{2g}}$ ratio is 0.39\ifmmode\pm\else\textpm\fi{}0.02. The measured saturation magnetization of this alloy is $0.114\ifmmode\pm\else\textpm\fi{}0.004 {\ensuremath{\mu}}_{B}$ per atom at 4.2\ifmmode^\circ\else\textdegree\fi{}K, which is considerably smaller than the total moment of $0.138 {\ensuremath{\mu}}_{B}$ seen by neutron diffraction. This discrepancy suggests a negative conduction-electron polarization of $\ensuremath{-}0.024\ifmmode\pm\else\textpm\fi{}0.011 {\ensuremath{\mu}}_{B}$ per atom. The temperature dependence of the magnetic scattering amplitude and the saturation magnetization indicate that the conduction-electron polarization disappears near the Curie temperature, which is about 55\ifmmode^\circ\else\textdegree\fi{}K. In addition, these data suggest that the $3d$ moment on an Fe atom and the $4d$ moments on surrounding Pd atoms are strongly coupled, although the range of the Pd polarization is not determined. The total $d$ moment associated with the moment cluster around each impurity site is $10.7\ifmmode\pm\else\textpm\fi{}0.6 {\ensuremath{\mu}}_{B}$.