High-Field Magnetization of Thulium Single Crystals

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°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 Néel temperature of 58°K with large anisotropy favoring the $c$ axis. They suggest that the antiferromagnetic structure below 58°K is an axial structure oriented along the $c$ axis. The low-field isofields for the $c$ axis show that at about 42°K the antiferromagnetic structure begins to square up, and at about 25°K the moments assume ferrimagnetic structure with a net moment along the $c$ axis at 4.2°K of $1.0{\mu }_B$ per atom. The ferrimagnetic coupling can be overcome by magnetic fields above 28 kOe, yielding a ferromagnetic structure with a saturation magnetization of $7.14{\mu }_B$ per atom. The $b$-axis sample, however, remained magnetically hard to the highest fields used; at 4.2°K the moment reached $0.75{\mu }_B$ per atom at 93 kOe. The data in the paramagnetic region gave a value for ${\mu }_{\mathrm{eff}}$ of $7.61{\mu }_B$, with paramagnetic Curie temperatures of ${\theta }_{11}=41\mathrm{}°$K, and ${\theta }_{\perp }=-17\mathrm{}°$K, where ${\theta }_{11}$ is for fields applied along the $c$ axis and ${\theta }_{\perp }$ is for fields applied perpendicularly to the $c$ axis.