Interpretation of the optical absorption spectrum and of the paramagnetic susceptibility of neodymium trifluoride

The absorption spectrum of single crystal NdF3 of tysonite structure was recorded at liquid helium temperature up to 33 800 cm−1. 127 Stark levels were obtained and fitted to a mean square deviation of 24 cm−1 with a Hamiltonian involving 12 free atom parameters and four D3h crystal field parameters. The fit was improved to a mean square deviation of 14 cm−1 by adding five supplementary crystal field parameters to approach the real C2 symmetry of the site. The paramagnetic susceptibilities parallel and perpendicular to the trigonal axis in the structure were measured from 4.2 to 1100 K and compared with the values derived from the wave vectors of the 18 lowest Kramers doublets through the application of the Van Vleck formula. An overall good agreement was found. The material is anisotropic, χ∥ being larger than χ⊥.