Paramagnetic susceptibility simulations from crystal field effects on Nd3+in magnesium borate MgNd(BO2)(5)

From the crystal field analysis of optical absorption spectra on monoclinic S.G. P2(1)/c MgNd(BO2)(5), where Nd3+ occupies a single crystallographic p osition with no symmetry elements, energy level schemes and an expression o f the associated wavefunctions for the 4f(3) configuration of Nd3+ have bee n derived, considering approximate C-2v and C-s (C-2) symmetries. Despite o f the low symmetry of Nd3+, resulting rms deviations between calculated and experimental levels are very satisfactory. The composition of the crystal field wavefunctions from both sets of phenomenological free-ion and crystal field parameters has been checked through a calculation of the thermal evo lution of the paramagnetic susceptibility chi, according to the Van Vleck f ormula. The same simulation was performed with crystal field parameters (CF Ps) resulting from the ab initio simple overlap model (SOM), considering th e Nd3+ real point symmetry, C-1. Over the whole measured range, 1.7-375 K, and especially at low temperatures, a very good reproduction of the experim ental chi vs. T is yielded by each of the experimental and SOM calculated c ollections of CFPs. The oversimplified SOM model seems thus to be useful pr oviding reasonable estimations of crystal field strength parameters. (C) 19 99 Elsevier Science B.V. All rights reserved.