Asphericity in the magnetization distribution of holmium

In a spiral magnetic structure an aspherical magnetic moment distribution around the ions gives rise to a new set of diffraction lines indexed as third-order satellites. Neutron-diffraction measurements have been made on single crystals of holmium and a Ho0.9Sc0.1 alloy to determine the magnetic structures as a function of temperature, and measure the intensities of the third-order satellites. From these intensities the experimental asphericity of the magnetization density is compared to that calculated with a single-ion model. The agreement between theory and experiment is qualitative; the experimental intensities being larger by a factor of approx. 1.5. The temperature dependence of the third-order satellite is in good agreement with a simple model proposing exchange splitting of the free-ion multiplet, with a negligible crystal-field interaction