Angle-dependent ESR results are given for 500-, 2500-, and 5000-ppm Er-doped YAl2 single crystals. An almost perfect analysis of the X- and Q-band data is achieved if the admixture of the first excited state Γ8(2) into the ground state Γ8(3) via the Zeeman interaction is taken into consideration. This enables us to determine the crystal electric field (CEF) parameter x=-0.322(20) and W=-0.29(2) K. The g-value shift yields N(EF)JΔg=+0.09(5) and the thermal broadening of the linewidth |N(EF)JΔH|=0.059(5). The precision of the experimental data allows, in principle, the determination of a hypothetical anisotropic exchange interaction. However, the fit yields an almost isotropic exchange interaction and upper limits for |N(EF)J4|≲5×10-5 and |N(EF)J6|≲6×10-8. This will be discussed in view of other results, i.e., DyPd. The effect of annealing of local defects on the CEF is discussed. In addition we observe and analyze for the first time the so-called cluster line in a Γ8 resonance and for high Er concentration. Briefly, we will present similar results on (ErSc)Al2 single crystals. In addition, we present a detailed theoretical calculation for impurity—conduction-electron and impurity-impurity relaxation for Γ8 resonances.
Döbler, U.; Baberschke, K.; and Barnes, S. E., "Γ8(3) Resonance in ESR of (ErY)Al2 Single Crystals" (1983). Physics Articles and Papers. 56.