Study of the ground multiplet of Kramers rare earth ions in solid matricesby multifrequency electron paramagnetic resonance spectroscopy:Nd~(3+)in PbWO_4single-crystals

摘要

A multifrequency electron paramagnetic resonance (EPR) investigation of Nd~(3+)impurities inPbWO_4single-crystals at the conventional microwave frequency (MF) 9.43 GHz, and at the 95, 190,and 285 GHz high frequencies was carried out. The resulting spectra are well described at allfrequencies by an axial spin-Hamiltonian corresponding to an effective electron spin of one-half andto a tetragonal symmetry. For the magnetic field along the tetragonal axis, the g11-factor and thehyperfine constant A_(11)of the lowest doublet ground multiplet decreases with frequencyincrease. For the magnetic field perpendicular to the tetragonal axis, the g1-factor exhibits a smallazimuthal angular dependence that increases with increasing the frequency due to the S_4sitesymmetry. The azimuthal angular dependence allows to clearly distinguish between different localaxial symmetries. These properties are interpreted as high field/frequency (HF) effects associatedwith the mixing by the large Zeeman interaction of some of the upper-lying doublets of the groundmultiplet into the lowest-lying doublet states. We show that from the combined analysis of themultifrequency MF- and HF-EPR spectra and of the optical data, an accurate description of theground multiplet of the Kramers rare earth ions in solid matrices can be derived.