SPIN-LATTICE INTERACTION FOR IONS IN LOW-SYMMETRY SITES - THE CASE OF MN2+CACO3

The spin-lattice interaction for Mn2+ ions as substitutional impurities in CaCO3 has been studied by electron-paramagnetic-resonance (EPR) experiments in crystals under externally applied uniaxial stresses. The shifts of the EPR lines of Mn2+ were measured as a function of the stress applied along the three different directions that accept uniaxial forces in this crystal. The values of six second-order spin-lattice coefficients for the Mn2+ site were obtained from the data. We also obtained two conditions relating linear combinations of the other four second-order coefficients. Contributions to the spin-lattice interaction of terms of fourth order in the effective spin have been detected. Our results are used to discuss the effect on the EPR spectrum of the different distortions of the carbonate ions surrounding the Mn2+.