Magnetic field dependent splitting of doubly degenerate phonon states in anhydrous cerium-trichloride

Abstract

The Raman spectra of single crystals of hexagonal CeCl₃ have been investigated atT=2K in external magnetic fieldsB up to 6 T. The crystal field states of the 4f ¹(² F _5/2)-configuration of Ce³⁺ show a linear Zeeman-splitting. Two degenerate phonon states (197 cm⁻¹(E _1g), 109 cm⁻¹(E _2g)) also split in the magnetic field. ForB parallel to the optic axisZ the field dependence of the splitting is similar to the behaviour reported earlier for Ce F₃ and NdF₃ (linear splitting at low fields, which is followed by a saturation at high fields). ForB⊥Z a splitting of the same phonons proportional toB ² is observed in CeCl₃, which was not found in the other compounds. The linewidths of the electronic transitions and of the split phonon components are reduced with increasing magnetic fieldstrength.

The field- and temperature dependences of the phonon energies can be explained quantitatively using results of the theory of the 4f-electron-phonon interaction as developed for the cooperative Jahn-Teller-effect or for the magneto-elastic interaction. The experimental results forB∥Z require an interaction Hamiltonian which is bilinear in the electronic and phonon operators, respectively. The conclusions are supported by group theoretical considerations.