High-Field Magnetization of Thulium Single Crystals

The magnetization of thulium has been measured along the 〈101̄0〉 (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 N\'eel 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 1.0μB per atom. The ferrimagnetic coupling can be overcome by magnetic fields above 28 kOe, yielding a ferromagnetic structure with a saturation magnetization of 7.14μB per atom. The b-axis sample, however, remained magnetically hard to the highest fields used; at 4.2^∘{}K the moment reached 0.75μB per atom at 93 kOe. The data in the paramagnetic region gave a value for μeff of 7.61μB, with paramagnetic Curie temperatures of θ₁₁=41^∘K, and θ_⊥=-17^∘K, where θ₁₁ is for fields applied along the c axis and θ_⊥ is for fields applied perpendicularly to the c axis.