High-Field Magnetization of Thulium Single Crystals

Abstract

The magnetization of thulium has been measured along the $〈10\overline{1}0〉$ ($b$ axis) and $〈0001〉$ ($c$ axis) directions from 4.2 to 300\ifmmode^\circ\else\textdegree\fi{}K in magnetic fields up to 100 kOe. The measurements were taken using a vibrating-sample magnetometer designed and constructed to operate in a 100-kOe superconducting solenoid. The data indicate a N\'eel temperature of 58\ifmmode^\circ\else\textdegree\fi{}K with large anisotropy favoring the $c$ axis. They suggest that the antiferromagnetic structure below 58\ifmmode^\circ\else\textdegree\fi{}K is an axial structure oriented along the $c$ axis. The low-field isofields for the $c$ axis show that at about 42\ifmmode^\circ\else\textdegree\fi{}K the antiferromagnetic structure begins to square up, and at about 25\ifmmode^\circ\else\textdegree\fi{}K the moments assume ferrimagnetic structure with a net moment along the $c$ axis at 4.2\ifmmode^\circ\else\textdegree\fi{}K of $1.0{\ensuremath{\mu}}_{B}$ per atom. The ferrimagnetic coupling can be overcome by magnetic fields above 28 kOe, yielding a ferromagnetic structure with a saturation magnetization of $7.14{\ensuremath{\mu}}_{B}$ per atom. The $b$-axis sample, however, remained magnetically hard to the highest fields used; at 4.2\ifmmode^\circ\else\textdegree\fi{}K the moment reached $0.75{\ensuremath{\mu}}_{B}$ per atom at 93 kOe. The data in the paramagnetic region gave a value for ${\ensuremath{\mu}}_{\mathrm{eff}}$ of $7.61{\ensuremath{\mu}}_{B}$, with paramagnetic Curie temperatures of ${\ensuremath{\theta}}_{11}=41\ifmmode^\circ\else\textdegree\fi{}$K, and ${\ensuremath{\theta}}_{\ensuremath{\perp}}=\ensuremath{-}17\ifmmode^\circ\else\textdegree\fi{}$K, where ${\ensuremath{\theta}}_{11}$ is for fields applied along the $c$ axis and ${\ensuremath{\theta}}_{\ensuremath{\perp}}$ is for fields applied perpendicularly to the $c$ axis.