Dynamic-nuclear-polarization method of investigating correlated ESR and NMR strain-broadening effects in single crystals

Quantitative theoretical and experimental investigations are made of the behavior of strain-broadened NMR line shapes under dynamic nuclear polarization (DNP) produced by microwave saturation at the centers of strain-broadened ESR lines where the ESR and NMR strain broadenings are mutually correlated. BAsed on a phenomenological model, analytical expressions are obtained for the shapes of the NMR lines under DNP. These expressions are found to be in good agreement with experimental data obtained from several ruby (${\mathrm{Al}}_2$ ${\mathrm{O}}_3$:${\mathrm{Cr}}^{3+}$) crystals.