Paramagnetic susceptibility simulations from crystal-field effects on rare-earth double molybdate and tungstate Na(5)RE(XO(4))(4)

Magnetic susceptibilities of polycrystalline samples of two series of double rare-earth molybdate and tungstate compounds, Na(5)RE(XO(4))(4) (RE = rare earth, X = Mo or W), with scheelite-type structure, space group I4(1)/a (No 88), where RE atoms adopt S-4 point symmetry, have been measured in the temperature range 1.7-400 K. Using the wavefunctions and energy levels derived from standard free-ion and crystal-field parameters deduced from the analysis of the optical spectra of some selected (Pr, Nd and Eu) compounds, a systematic calculation of the temperature-dependent paramagnetic susceptibility, for all 4f(N) rare-earth configurations on the two series, has been carried out according to the Van Vleck formula. Very good agreements with experimental data are found over the whole temperature range. The standard crystal-field treatment of 4f(N) ions is shown to explain the magnetic properties of these compounds, for which no kind of magnetic interaction among the rare-earth ions has been detected.