Orbital magnetization in CoCl^2-₄ and Co(phthalocyanine) from polarized neutron diffraction

Abstract

Spin-orbit coupling introduces orbital angular momentum into the ⁴ A ₂ (CoCl^2- ₄) or ²B_2g (Co(Pc)) ground term of the Co²⁺ ion. Using a ligand field model real space magnetization densities and magnetic structure factors for the crystals are calculated. The shape of the magnetization and its non-collinearity with the magnetic field make the magnetic structure factors more complicated than is usually assumed in treating polarized neutron diffraction data for transition metal ions. However, it is found that for Cs₃CoCl₅ a systematic cancellation of correcting terms leads to results not distinguishable from those of the usual ‘dipole’ correction within the experimental errors. For Co(Pc) the ‘anomalous’ orbital scattering effects are larger and would be important if the data set were as accurate as that for Cs₃CoCl₅. An improved correction mechanism for PND data is developed but does not lead to significant changes in the valence orbital populations previously derived for the two compounds. Such corrections are, however, likely to be useful in other systems where orbital scattering effects are present.