Linewidth of the Electron Paramagnetic Resonance of ${\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)}_{1-x}{\left({\mathrm{Cr}}_2{\mathrm{O}}_3\right)}_x$

The linewidth variation of electron-paramagnetic-resonance (EPR) absorption in single crystals of ${\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)}_{1-x}{\left({\mathrm{Cr}}_2{\mathrm{O}}_3\right)}_x$ with $x$ equal to 0.01, 0.001, or 0.0001% has been investigated as a function of the angle between the $C$ axis of the samples and the magnetic field. The observed width variation is practically independent of the values of $x$ and of the choice of the axis of rotation perpendicular to both the $C$ axis and the magnetic field. In order to account for the observed width variation, three alternative models have been considered: a mosaic model, a strain model, and a hybrid of the two models. The calculated width variation based on each of the three models is in qualitative agreement with the observed one, the degree of agreement being the best for the strain model. Quantitatively, however, significant discrepancies between the observed and calculated variations have been found for some regions of the angle of rotation. Some discussions of the discrepancies are presented.