Influence of Strains on Paramagnetic-Resonance Spectrum for Strongly Coupled Ions—Application toV3+in MgO

We develop a Monte Carlo method to study the influence of static random strains on EPR and acoustic-paramagnetic-resonance (APR) spectra. The method consists of calculating the line shape using random numbers which represent the random strains. We have applied this method to the particular case of a $S=1\mathrm{}$ system in cubic symmetry in the presence of ${\Gamma }_{3g}$-type strains. The important parameter is the product of the strain-ion coupling coefficient and the width of the distribution function of the strains. When this parameter is small compared to the Zeeman term, we find the known results obtained using perturbation theory. When this parameter is of the order of the Zeeman term, the line shape is profoundly modified and the spectrum has great similarity to an axial spectrum. The comparison between calculated and experimental spectra obtained with MgO: ${\mathrm{V}}^{3+}$ confirms the previously proposed interpretation. The strain-ion coupling coefficient is deduced from this comparison. We also discuss the possibility of deducing the Jahn-Teller energy and covalency from our recent experimental results interpreted within the model developed here. The values obtained show that Jahn-Teller coupling is only slightly greater than spin-orbit coupling. Thus, the MgO: ${\mathrm{V}}^{3+}$ system appears to be near the limit where the Jahn-Teller effect is stabilized by spin-orbit coupling.