Dipole interaction and magnetic anisotropy in gadolinium compounds

The influence of the dipole interaction on the magnetic anisotropy of Gd compounds is investigated. Available data on ferromagnets and antiferromagnets with different crystal structures are discussed and complemented by new neutron scattering experiments on ${\mathrm{GdCu}}_2\mathrm{In},$ ${\mathrm{GdAu}}_2{\mathrm{Si}}_2,$ ${\mathrm{GdAu}}_2,$ and ${\mathrm{GdAg}}_2.$ If the propagation vector of the magnetic structure is known, the orientation of the magnetic moments as caused by the dipole interaction can be predicted by a straightforward numerical method for compounds with a single Gd atom in the primitive unit cell. The moment directions found by magnetic diffraction on ${\mathrm{GdAu}}_2{\mathrm{Si}}_2,$ ${\mathrm{GdAu}}_2,$ ${\mathrm{GdAg}}_2,$ ${\mathrm{GdCu}}_2{\mathrm{Si}}_2,$ ${\mathrm{GdNi}}_2{\mathrm{B}}_2\mathrm{C},$ ${\mathrm{GdNi}}_2{\mathrm{Si}}_2,$ ${\mathrm{GdBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7,$ ${\mathrm{GdNi}}_5,$ GdCuSn, ${\mathrm{GdCu}}_2\mathrm{In},$ ${\mathrm{GdCu}}_4\mathrm{In},$ and $\mathrm{Gd}X$ $(X=\mathrm{Ag},$ Cu, S, Se, Sb, As, Bi, P) are compared to the predicted directions resulting in an almost complete accordance. Therefore, the dipole interaction is identified as the dominating source of anisotropy for most Gd compounds. The numerical method can be applied to a large number of other compounds with zero angular momentum.