The Paramagnetic Form Factor of Gadolinium

Abstract

A sample of Gd₂O₃ enriched to about 98% in the low absorbing isotope ¹⁶⁰Gd was examined by neutron diffraction at temperatures from room temperature to 1.3°K. Measurements of the diffuse background scattering in the high and intermediate temperature patterns have been used to obtain the paramagnetic form factor as a function of sinθ/λ. The observed scattering cross section was converted to f² values by assuming the full theoretical paramagnetic moment of g[J(J+1)]^1/2 for Gd⁺³ and using this value to correct for the isotropic nonmagnetic part of the scattering. The form factor obtained in this manner is near the calculated Hartree‐Fock free‐atom form factor but appears to be slightly higher over most of the region out to sinθ/λ≅0.3 Å⁻¹. Beyond this value, overlapping nuclear reflections in the powder pattern make it impossible to obtain usable values of the background intensity. Magnetic ordering of a complex antiferromagnetic nature appears at about 1.6°K but a large diffuse hump in the pattern remains to a few degrees above liquid‐helium temperature. This hump never completely disappears at the lowest temperatures reached indicating the magnetic structure is by no means fully developed at 1.3°K.