Direct observation of the discrete energy spectrum of two lanthanide-based single-chain magnets by far-infrared spectroscopy

The far-infrared optical transmission has been studied for two lanthanide-based single-chain magnets DyPhOPh and TbPhOPh in the frequency range between 3 and 80 cm−1. The spectra were acquired at temperatures between 2 and 80 K and magnetic fields up to 6 T. Based on their magnetic field dependence in DyPhOPh two of the observed absorption lines are identified as transitions inside the crystal field split Dy3+ ground multiplet 6H15/2, coupled to the neighboring spins. In TbPhOPh one transition was observed inside the crystal-field-split Tb3+ ground multiplet 7F6. The results allow a spectroscopic investigation of the role of single-ion anisotropy and exchange in Glauber dynamics.