Magnetic Structures of Metallic Erbium

Single-crystal neutron-diffraction data were obtained for metallic erbium at sample temperatures from 4.2 to 298^∘{}K. Three distinct regions of long-range magnetic order were observed. In the high-temperature region (52-80^∘{}K) 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^∘{}K with μz(max)=7.6 μB{Er}³⁺. Below 52^∘K the basal-plane component of the moment begins to order, and a third-order modulation along thec$ 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^∘{}K) a ferromagnetic spiral structure is indicated. At saturation the ferromagnetic c-axis component is 7.9 μB{Er}³⁺$ and the spiral basal-plane component is $4.3{{μ}}B/{Er}³⁺$. The total ordered moment is then the free-ion value of $9.0{{μ}}B/{Er}³⁺$.