Effect of Applied Electric Fields on the Electron Spin Resonance of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ in $\alpha$-${\mathrm{Al}}_2$${\mathrm{O}}_3$

The effect of applied electric fields in broadening the electron spin resonance lines of the isoelectronic ions ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ in $\alpha$-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ has been observed. This is interpreted as an unresolved line "splitting" which is linear in the applied field. The change in the spin Hamiltonian $D$ parameter with applied field parallel to the $c$ axis ($\frac{\partial D}{\partial E}$) is 1.00±0.09 for ${\mathrm{Fe}}^{3+}$ and 1.03±0.09 for ${\mathrm{Mn}}^{2+}$ in units of ${10}^{-5\mathrm{}}$ G cm/V. The existence of this effect implies that these ions replace ${\mathrm{Al}}^{3+}$ ions substitutionally in the $\alpha$-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ lattice. A simplified calculation indicates that ionic displacement plays an important role in producing the effect in these $S$-state ions and thatthe resultant relative change in the even component of the axial crystalline field appears to be much larger for ${\mathrm{Mn}}^{2+}$ than ${\mathrm{Fe}}^{3+}$.