Magnetic Structures of Holmium. I. The Virgin State

Abstract

Neutron-diffraction measurements have been made on single-crystal specimens of holmium at temperatures ranging from room temperature to 4.2\ifmmode^\circ\else\textdegree\fi{}K. Below the N\'eel temperature of 133\ifmmode^\circ\else\textdegree\fi{}K, the moments order in a helical structure in which the $c$ axis is the screw axis. The interlayer angle varies from about 50\ifmmode^\circ\else\textdegree\fi{} per layer at ${T}_{N}$ to 30.0\ifmmode^\circ\else\textdegree\fi{} per layer at 4.2\ifmmode^\circ\else\textdegree\fi{}K. Below about 20\ifmmode^\circ\else\textdegree\fi{}K the structure is a conical configuration in which there is a net moment of $1.7{\ensuremath{\mu}}_{B}$ parallel to the $c$ axis. The configuration of moments in the basal plane at 4.2\ifmmode^\circ\else\textdegree\fi{}K is a distorted helical one in which moments of $9.5{\ensuremath{\mu}}_{B}$ are bunched around the easy $b$ directions in the plane.