Spin-Density Distribution in CuCl2·2D2O

The spin-density distribution in antiferromagnetic Cu${\mathrm{Cl}}_2$·2${\mathrm{D}}_2$O has been investigated at 1.7°K by neutron diffraction measurements. No appreciable concentrations of spin density were found except those localized about the ${\mathrm{Cu}}^{++}$ positions. The Fourier maps used in analyzing the neutron data did disclose a markedly aspherical distribution for the ${\mathrm{Cu}}^{++}$ spin density, however. A satisfactory explanation for the asphericity was obtained by consideration of the ground-state wave function of ${\mathrm{Cu}}^{++}$ in an orthorhombic crystalline field. The resulting wave function was found to consist of an admixture of two $d\gamma$ orbitals, about $90\%(x^2-y^2)$ and $10\%(3z^2-r^2)$. The neutron study also confirms the existence of a weak antiferromagnetic spin component, as predicted theoretically by Moriya. The form factor for this component is quite anomalous, however, indicating that it does not arise from a simple canting of the ionic moment.