Magnetic Susceptibility of Yb3+ in an Octahedral Environment

The magnetic susceptibility of Yb³⁺ in Cs₂NaYbCl₆ was measured from 2.5 to 100°K and showed Curie–Weiss temperature dependence from 2.5 to 20°K ${\mathrm{(\mu }}_{\mathrm{eff}}{\text{\hspace{0.17em}=\hspace{0.17em}2.46 μ}}_B\text{, θ\hspace{0.17em}=\hspace{0.17em}0.95°}\mathrm{C})$ and from 45 to 100°K ${\mathrm{(\mu }}_{\mathrm{eff}}{\text{\hspace{0.17em}=\hspace{0.17em}4.47 μ}}_B\text{, θ\hspace{0.17em}=\hspace{0.17em}70°}\mathrm{C})$ , with a transitional region from 20–45°K. From a comparison of the experimental results with theoretical results for a $\text{J\hspace{0.17em}=\hspace{0.17em}7\hspace{0.17em}/\hspace{0.17em}2}$ ion in an octahedral field, the two crystalline field levels observed were identified as a ${\Gamma }_6$ ground level, and a ${\Gamma }_8$ level about 60 cm⁻¹ higher. The energy separation between the ${\Gamma }_6$ and ${\Gamma }_8$ levels and a ratio of the crystalline field parameters ${\mathrm{-\hspace{0.17em}b}}_4{\mathrm{\hspace{0.17em}/\hspace{0.17em}b}}_6$ derived from other measurements were employed to deduce ${\mathrm{-\hspace{0.17em}b}}_4{\text{\hspace{0.17em}=\hspace{0.17em}4.8}}_5{\text{–4.9}}_5$ and $b_6\text{\hspace{0.17em}≈\hspace{0.17em}0.05\hspace{0.17em}−\hspace{0.17em}0.002}{\mathrm{cm}}^{\text{−1}}$ . From these parameters, a ${\Gamma }_7$ level at ∼ 160 cm⁻¹ is predicted. A covalent contribution to the ${\Gamma }_6$ ground level is considered.