Effects of magnetic bonding in rare earth transition metal intermetallics

摘要

Neutron diffraction experiments on rare-earth transition metal magnetic alloys Er(sub 2)Fe(sub 14)B and Er(sub 2)Fe(sub 17) have been carried out at temperature above and below the ordering temperature ((Tc)). An anomalously large magnetic moment is observed at the crystallographic j(sub 2) site in Er(sub 2)Fe(sub 14)B which is the intersection point of the major ligand lines in the crystal structure. The interatomic Fe-Fe distances are in the range of strong ferromagnetic bonds ((ge) 2.66 (angstrom)). The analogous f site in Er(sub 2)Fe(sub 17) does not develop as large a magnetic moment. In addition, the same sites show strong preference for Fe atoms in the respective substituted compounds. Due to poor phase stability of Er(sub 2) (Co(sub x)Fe(sub 1 (minus)x))(sub 14)B compounds, iron substitution has been studied in detail in Er(sub 2)(Co(sub x)Fe(sub 1 (minus)x))(sub 17) alloys for site specific order an lattice distortion effects. However, a nonlinear change in the c lattice parameter observed in the neutron diffraction results cannot be explained on the basis of site preference alone. The neutron refinement results indicate iron rich compositions in Er(sub 2)(Co(sub x)Fe(sub 1 (minus)x))(sub 17) materials, which is related to random substitution of Fe dumbbell pairs in the rare earth sites in the lattice. However, extensive electron microscopy (selected area electron diffraction and high resolution imaging) of Er(sub 2)Fe(sub 17) and Er(sub 2)(Co(sub .40)Fe(sub .60)) (sub 17) failed to reveal any microscopic inhomogeneity. 12 refs., 5 figs., 2 tabs.