Neutron magnetic scattering from rare-earth ions

The theory of neutron scattering by paramagnetic rare-earth ions has been given by Trammell and more recently by Odiot and Saint-James. Unlike the case for the iron series transition metals, for which the orbital angular momentum of the 3d electrons is almost completely quenched, the magnetic scattering of neutrons from the rare earths (except for gadolinium and europium) arises from both the spin and orbital contributions to the magnetization. Using recently determined Hartree-Fock wave functions for some of the trivalent rare-earth ions we have determined the functions 〈j_n〉 and 〈g _n〉 (for n=0, 2, 4, and 6) which are necessary for the theoretical evaluation of the spin and orbital contributions respectively to the magnetic form factor. A comparison of these theoretical results with the experiments of Koehler and Wollan for Nd³⁺ and Er³⁺ and of Koehler, Wollan and Wilkinson for Ho³⁺ is presented. Differences are found between theory and experiment and some possible reasons for this are discussed. A paper on these matters is being submitted to the Physical Review.