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Single-crystal neutron-diffraction data were obtained for metallic erbium at sample temperatures from 4. 2 to 298^. Three distinct regions of long-range magnetic order were observed. In the high-temperature region (52-80^) the ordered moments are confined to the c-axis direction and are sinusoidally modulated with a modulation wavelength of 3. 5C₀. The amplitude of this modulation saturates at 52^ with ₙ (max) =7. 6 ₁Er^3+. Below 52^ the basal-plane component of the moment begins to order, and a third-order modulation along the c axis is observed. These effects are interpreted on the basis of a squared elliptical spiral with its major axis tilted relative to the crystal c axis. However, the structural details in this region are obscured by a temperature variation of the modulation wavelength and by the incommensurability of the modulation and the lattice. In the low-temperature region (4. 2-20^) a ferromagnetic spiral structure is indicated. At saturation the ferromagnetic c-axis component is 7. 9 ₁Er^3+ and the spiral basal-plane component is 4. 3₁/Er^3+. The total ordered moment is then the free-ion value of 9. 0₁/Er^3+.
Cable et al. (Mon,) studied this question.