CRYSTAL-FIELD EFFECT ON THE MAGNETIC-SUSCEPTIBILITY OF RARE-EARTH (PR, ND, EU) MIXED OXIDES

The comparison between the experimental and calculated magnetic susceptibility of pr(3+), Nd3+, and Eu3+ compounds in a wide group of materials, scheelite-type Na(5)RE(MoO4)4, S.G. I4(1)/a (No. 88), cubic RE(3)Sb(5)O(12), S.G. I43m (No. 217), monoclinic RE(2) Te4O11, S.G. C2/c (No. 15), and hexagonal RE(3)WO(6)Cl(3), S.G. P6(3)/m (No. 176) is reported. Structural and optical studies have shown that in every case the rare earth occupies one single crystallographic position, whose point symmetries are going from a relatively high symmetry, S-4 for both Na(5)RE(MoO4)(4) and RE(3)Sb(5)O(12) compounds, to very low symmetries, C-s and C-1 for RE(3)WO(6)Cl(3) and RE(2)Te(4)O(11), respectively. The magnetic susceptibilities have been measured in the temperature range 4.2-300 K. The experimental spectroscopic data were analyzed in terms of crystal-field theory for the 4f(2), 4f(3), and 4f(6) configurations of the triply ionized Pr, Nd, and Eu ions, and then, using the wavefunctions associated with each energy level obtained from these analysis, the corresponding magnetic susceptibilities and their evolution vs temperature were simulated according to the van Vleck formalism. Satisfactory correlations, especially for Nd and Eu compounds, were achieved between the experimental and calculated magnetic susceptibilities, even when the approximate D-2d (near S-4) and C-2v and/or C-s (close to C-1) potentials were considered. Their observed deviation from the Curie-Weiss behavior at low temperature, very well reproduced, reflects the splitting of the ground state associated with these cations under the influence of the crystal field and is not due to any sort of magnetic interaction between the magnetic ions. (C) 1995 Academic Press, Inc.