Sign of the Crystalline Cubic Field Splitting Parameterain anSState

Measurements of the paramagnetic resonance spectrum of manganese and ferric ions at low temperatures yield the values for the cubic field splitting parameter $a$ as 18.6×${10}^{-4\mathrm{}}$ and 205×${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ respectively. The sign of $a$ is positive in both cases, indicating that the twofold degenerate level is lower than the fourfold degenerate level. This is in contrast with Bleaney and Trenam's results on ferric alums who find a negative $a$. For gadolinium in Ca${\mathrm{F}}_2$, the constant $a=175\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and is also positive.