Multifrequency electron paramagnetic resonance of Ce3+ in the Gd(HBPz3)2 tropolonate complex: high-field effects.

An electron paramagnetic resonance (EPR) powder spectrum investigation of rare earth trace impurities in the Gd(HBPz(3))(2) tropolonate complex (GdTrp) was carried out at 95, 190, and 285 GHz. Ce3+, ion impurities were identified by EPR transitions between levels of the two lowest-lying doublets of the ground J = 5/2 manifold. An important frequency and magnetic-field dependence of the g-factor was observed. The system was successfully described by a Hamiltonian appropriate for tetragonal symmetry without orthorhombic distortion. Compared to conventional microwave EPR spectroscopy, at high fields these effective g-values depend not only on the polar angle between the magnetic field B and the tetragonal axis, but also on the azimuthal angle phi between B and the binary axes of the molecular complex. These dependences include additional terms proportional to (B)(2m), (cos4 phi)(n), where m >= n are natural numbers. They show that in the present experiment, the Zeeman interaction is comparable with the zero-field splitting of the ground manifold. It is found that the second, and the third doublet are located at 13.98 +/- 0.25 cm(-1) and 9.32 +/- 0.15 cm(-1) above the first one, respectively.