Structural and magnetic properties of iron-rich compounds in the Yb-Fe-Al system

The iron-rich corner of the Yb-Fe-Al phase diagram at 500 degreesC contains at least four distinct ternary phases having closely related crystal structures. Two have hexagonal symmetry and are derived from the LuFe9.5 type (0-26 at.% Al) and TbCu7 type structure (11-13 at.% Al), and two have rhombohedral symmetry and are derived from the PrFe7 type structure (10-32 at.% Al). As the aluminum content is increased the subcell volumes increase while the subcell c/a ratios decrease. Ytterbium atoms and iron dumbbells substitute each other at various proportions such that the hexagonal structures have the highest and the rhombohedral structures the lowest dumbbell concentration. Aluminum substitutes iron preferentially on non-dumbbell sites and occupies dumbbell sites only at high overall aluminum contents. The compounds are ferromagnetic and show magnetizations of up to sigmasimilar to50 emu/g at 10 kOe at intermediate aluminum contents 14-24 at.% Al) and magnetic ordering temperatures of up to 80 degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.