High-Field Destruction of the Nonmagnetic Ground State in TmN

The octahedral cubic symmetry at a Tm site in TmN gives a singlet (nonmagnetic) level as the ground state of the Tm3+ ion in the crystal field. We have used pulsed magnetic fields up to 265 kOe to counteract the crystal-field effects and induce large ionic moments. Magnetizations measured at 4.2°, 20.4°, and 77°K show an approach to saturation at the highest fields used. For 4.2°K, the moment at 265 kOe is 4.5 μB per molecule as compared to the saturation value of 7 μB. The experimental results for the magnetization and susceptibility are compared to the theoretical results for crystal-field calculations. This comparison enables us to discuss the way in which exchange forces enter the magnetization process at high magnetic fields as the ground state becomes polarized. The fourth- and sixth-order crystal-field parameters have been evaluated by observing paramagnetic resonance at 9.35 Gc/sec for the Γ5(2) excited triplet.