Magnetic Structures of Metallic Erbium

Abstract

Single-crystal neutron-diffraction data were obtained for metallic erbium at sample temperatures from 4.2 to 298\ifmmode^\circ\else\textdegree\fi{}K. Three distinct regions of long-range magnetic order were observed. In the high-temperature region (52-80\ifmmode^\circ\else\textdegree\fi{}K) the ordered moments are confined to the $c$-axis direction and are sinusoidally modulated with a modulation wavelength of $3.5{C}_{0}$. The amplitude of this modulation saturates at 52\ifmmode^\circ\else\textdegree\fi{}K with ${\ensuremath{\mu}}_{z}(max)=7.6$ ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$${\mathrm{Er}}^{3+}$. Below 52\ifmmode^\circ\else\textdegree\fi{}K the basal-plane component of the moment begins to order, and a third-order modulation along the $c$ axis is observed. These effects are interpreted on the basis of a squared elliptical spiral with its major axis tilted relative to the crystal $c$ axis. However, the structural details in this region are obscured by a temperature variation of the modulation wavelength and by the incommensurability of the modulation and the lattice. In the low-temperature region (4.2-20\ifmmode^\circ\else\textdegree\fi{}K) a ferromagnetic spiral structure is indicated. At saturation the ferromagnetic $c$-axis component is 7.9 ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$${\mathrm{Er}}^{3+}$ and the spiral basal-plane component is $4.3{\ensuremath{\mu}}_{B}/{\mathrm{Er}}^{3+}$. The total ordered moment is then the free-ion value of $9.0{\ensuremath{\mu}}_{B}/{\mathrm{Er}}^{3+}$.