Calculations of spin Hamiltonian parameters and analysis of trigonal distortions in LiSr(Al,Ga)F₆:Cr³⁺ crystals

The effective spin-Hamiltonian (SH) parameters (zero-field splitting D and g factors g_∥ and g_⊥) for Cr³⁺ ions in LiSr(Al,Ga)F₆ crystals are calculated from the complete high-order perturbation formulae for a d³ ion. Parameters of trigonal crystal field acting on the Cr³⁺ ion are calculated. The magnitude of trigonal distortion of the [CrF₆]^3- clusters is related to the experimental measurements of the spin-Hamiltonian parameters in the considered systems. Since in both crystals g_∥<g_⊥, [CrF₆]^3- clusters undergo an axial compression along the C₃ axis. Experimental values of the hyperfine structure constants A_∥ and A_⊥ are used to evaluate the core polarization constant κ for Cr³⁺ ion in both crystals.