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°K. Below the Néel temperature of 133°K, the moments order in a helical structure in which the $c$ axis is the screw axis. The interlayer angle varies from about 50° per layer at $T_N$ to 30.0° per layer at 4.2°K. Below about 20°K the structure is a conical configuration in which there is a net moment of $1.7{\mu }_B$ parallel to the $c$ axis. The configuration of moments in the basal plane at 4.2°K is a distorted helical one in which moments of $9.5{\mu }_B$ are bunched around the easy $b$ directions in the plane.