The magnetization distributions in some Heusler alloys proposed as half-metallic ferromagnets

Abstract

The magnetization distributions in a series of ternary intermetallic compounds based on the composition Co 2 YZ where Y is Ti, Mn or Fe and Z a subgroup-B element have been determined from polarized neutron diffraction measurements. Comparison of the magnetic structure factors with model calculations shows that the magnetization is associated principally with those atoms which in their elemental state are themselves magnetic. The observed deviations of the magnetic moment distributions from spherical symmetry have been used to deduce which of the 3d sub-bands are active at the Fermi energy. A small moment close to the limits of resolution is observed at some of the Z sites, together with a small delocalized moment which in most cases is negative. The results have been compared with the predictions of band models, which indicate that the Fermi level falls in a broad minimum in the minority-spin density of d states. Although the identity of the bands active at the Fermi surface is in broad agreement with predictions of band-structure calculations (Ishida S, Akazawa S, Kubo Y and Ishida J 1982 J. Phys. F: Met. Phys. 12 1111), the results suggest that there is a finite density of states in the minority-spin d band of manganese. Hence the compounds cannot be classified as half-metallic ferromagnets.