The Jahn-Teller theory and calculations of the relaxation time and resonance lineshape for Fe²⁺ions in Al₂O₃

Existing experimental data for the ground states of Fe 2+ :Al 2 O 3 are accounted for by a multimode dynamic Jahn-Teller model in which an Fe 2+ ion substitutes for an Al 3+ ion. The first- and second-order Jahn-Teller reduction factors are found to be gamma =0.19, F a = 0.0015 (cm -1 ) -1 and F b =0.0024 (cm -1 ) -1 and satisfactorily account for the quenching of the trigonal field. The relaxation time T 1 , of the Fe 2+ ion is then calculated to be approximately 2 mu s at 1.2K confirming that the Fe 2+ ion is strongly coupled to the Al 2 O 3 lattice. The main contribution to T 1 is from the E theta , E epsilon components of the lattice momentum acting through the spin-orbit coupling and trigonal-field perturbations. The contributions to T 1 from displacements due to other lattice modes are found to be smaller. An analysis of the APR or EF-EPR lineshape on the Jahn-Teller model is in agreement with all the experimental data.