Effects of the fine and hyperfine interactions in the EPR spectrum of the γ8 quartet (Pd:Er)

Measurements of the angular dependence of the EPR spectrum of the quartet Γ8 ground state Pd:Er3+ are reported. An asymmetric angular dependence of the 1 2 and 3 4 transitions was observed in the (110) plane in some crystals. The asymmetric as well as the symmetric behavior of the angular dependence are explained by the trigonal deformation of samples. The axial crystalline-field parameter D is obtained by comparing the asymmetric behavior with the theoretical calculations, D-33 G. The theory of the hyperfine spectrum of the Γ8 quartet is developed. A good agreement with the experimental field position (as measured by Devine and Moret) for the allowed hyperfine spectra is achieved by the introduction of the interference-quadrupole-magnetic-hyperfine- interaction terms. The quadrupole constant B for Er167 in Pd is obtained giving BgJμB=-0.5±0.1 G. It is shown that the presence of the strong forbidden hyperfine spectrum confirms the existence of trigonal deformation. A general and convenient formula for the intensities of the hyperfine spectra is obtained. The forbidden intensities are explained by the induced axial quadrupole interaction together with the deformation of the electronic functions of the Γ8 quartet caused by the trigonal deformation. The importance of the Δm=±2 transitions is demonstrated by the calculation of the pair structure of all the forbidden transitions. The influence of the anisotropic exchange interaction with the conduction electrons on the hyperfine splitting of the Γ8 quartet is discussed.