A polarized neutron study of the magnetization distribution in Co ₂FeSi

The magnetization distribution in Co₂FeSi which has the largest moment per formula unit ∼6 μ_B of all Heusler alloys, has been determined using polarized neutron diffraction. The experimentally determined magnetization has been integrated over spheres centred on the three sites of the L1₂ structure giving μ Fe = 3.10(3) μ_B and μ Co = 1.43(2) μ_B, results which are slightly lower than the moments in atomic spheres of similar radii obtained in recent LDA + U band structure calculations (Li et al 2010 Chin. Phys. B 19 097102). Approximately 50% of the magnetic carriers at the Fe sites were found to be in orbitals with e _g symmetry. This was higher, ≃65%, at the Co sites. Both Fe and Co were found to have orbital moments that are larger than those predicted. Comparison with similar results obtained for related alloys suggests that there must be a finite density of states in both spin bands at the Fermi energy indicating that Co₂FeSi is not a perfect half-metallic ferromagnet.