EPR Studies of Excited State Exchange and Crystal-Field Effects in Rare Earth Compounds

摘要

EPR in excited crystal-field states of Tm exp 3+ , Pr exp 3+ , and Tb exp 3+ in singlet-ground-state systems and in the excited state of Ce exp 3+ in CeP are reviewed. Because one is looking at a crystal-field excited state resonance, the exchange, even if isotropic, does not act as a secular perturbation. This means that one obtains different effects and has access to more information about the dynamic effects of exchange than in conventional paramagnetic resonance experiments. The Tm and Pr monopnictides studied are paramagnetic at all temperatures. The most striking feature of the behavior of the GAMMA sub 5 /sup (2)/ EPR in the Tm compounds is the presence of an anomalous maximum in the temperature dependence of the g-factor. The relationship of this effect to anisotropic exchange is discussed. The results of the EPR of the excited GAMMA sub 5 /sup (2)/ level of Tb sub 3+ (g-factor becomes very large at T/sub N/ in antiferromagnetic TbX (X = P, As, Sb) and that of the excited GAMMA sub 8 level of Ce exp 3+ in antiferromagnetic CeP will also be reported. For sufficient dilution of the Tb exp 3+ in the terbium monopnictides, the systems become paramagnetic (Van Vleck paramagnets) down to 0 exp 0 K. The Tb exp 3+ excited state resonance EPR in Tb/sub 0.1/ La/sub 0.9/P was studied as an example of behavior in such systems. 10 fig. (ERA citation 01:026160)