Influence of cubic crystal field on the magnetic susceptibility of defect-perovskite RTa3O9 (R = rare earth)

Perovskite-related compounds RTa3O9 (R = rare earth elements except Sc, Pm, Yb, Lu) have been prepared and magnetic susceptibility measurements have been carried out. The characteristic behavior in the temperature dependence of the susceptibility for each sample has been analyzed in terms of the crystalline electric field of cubic symmetry yielded from the nearest neighboring 12 O2- and the next-nearest neighboring eight Ta5+ around R3+ ions. These analytical results demonstrate clearly that the contribution of the next-nearest neighbors to the susceptibility is important and fairly large because of the high valence state of Ta5+. The ground states of R3+ ions in the compounds are determined as follows in the Bethe's notation: Ce3+, Gamma(8); Pr3+, Gamma(3): Nd3+, Gamma(6); Tb3+, Gamma(5); Dy3+, Gamma(8); Ho3+, Gamma(5); Er3+, Gamma(8); and Tm3+, Gamma(5). The precise analysis for RTa3O9 based on the crystal field theory has systematically provided the energy splitting scheme, the f-electron wave functions and significant crystalline field parameters containing both fourth and sixth order terms. The splitting into Gamma(6), Gamma(7) and Gamma(8) from the degenerated ground state S-8(7/2) of Gd3+ is negligibly small and not distinguishable above 2 K. (C) 1999 Elsevier Science Ltd. All rights reserved.