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

Abstract

Existing experimental data for the ground states of Fe²⁺:Al₂O₃ are accounted for by a multimode dynamic Jahn-Teller model in which an Fe²⁺ ion substitutes for an Al³⁺ 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 T₁, of the Fe²⁺ ion is then calculated to be approximately 2 mu s at 1.2K confirming that the Fe²⁺ ion is strongly coupled to the Al₂O₃ lattice. The main contribution to T₁ 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 T₁ 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.