Uniaxial-stress effect of the EPR spectra of magnetic impurities inSrCl2

In this paper we present the results of uniaxial-stress-effect experiments in EPR on ${\mathrm{SrCl}}_2$ crystals doped with different kinds of magnetic impurities: ${\mathrm{Mn}}^{2+}$, ${\mathrm{Co}}^{2+}$, and ${\mathrm{Eu}}^{2+}$. The impurities ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Co}}^{2+}$ are appreciably smaller than the cation (${\mathrm{Sr}}^{2+}$) of the host crystal, whereas ${\mathrm{Sr}}^{2+}$ and ${\mathrm{Eu}}^{2+}$ have about the same size. It appears that the uniaxial-stress effect of the smaller-sized impurities is much larger than expected on the basis of the elastic properties of the ${\mathrm{SrCl}}_2$ single crystal. Local deformations in the neighborhood of these impurities play a decisive role. Earlier electric-field-effect experiments carried out in our laboratory have shown that substitutional ${\mathrm{Mn}}^{2+}$ impurities in ${\mathrm{SrCl}}_2$ are located in a rather shallow potential well, which can be modified significantly by means of an external electric field. This observation is supported by the behavior of the crystal-field splitting and the uniaxial-stress effect as a function of the temperature observed in the present investigation.