Ferromagnetic Gd$_{100-x}$Fe$_{x}$ (x = 4 - 40) Nanostructures

Iron in concentrations as small as 4 at. {\%} (where the distance between Fe atoms is more than three lattice spacings) produces ferromagnetic behavior at temperatures up to 50 K above the Gd Curie temperature T$_{C}$ in Gd$_{100-x}$Fe$_{x}$ nanostructures. X-ray diffraction and XAFS show that Gd$_{100-x}$Fe$_{x}$ nanostructures made by inert-gas-condensation and melt-spinning have nanoscale hcp Gd grains with Gd-Fe grain boundaries. Magnetization and XMCD measurements indicate that, above the bulk Gd T$_{C, }$Fe atoms polarize Gd atoms and produce ferromagnetic behavior with coercivities on the order of 50-100 Oe. The coercivity decreases as the temperature decreases toward the Gd T$_{C, }$which we attribute to random anisotropy averaging produced by ordering of the hcp-Gd grains.