Effects of electron correlation in crystal-field splittings of Sm2+ in MFCl-type hosts.

Abstract

Effects of pressure on the crystal-field splittings of the $^{5}$${\mathit{D}}_{1}$ and $^{7}$${\mathit{F}}_{1}$ multiplets were studied for ${\mathrm{Sm}}^{2+}$ in MFCl (M=Ba, Sr, and Ca). A comparison with experimental data from the literature for ${\mathrm{Eu}}^{3+}$ in different compounds at ambient pressure and partly under pressure shows that the splittings of $^{5}$${\mathit{D}}_{1}$ and $^{7}$${\mathit{F}}_{1}$ are successfully explained in the case of ${\mathrm{Eu}}^{3+}$ by the spin-correlated crystal-field (SCCF) model, when a constant SCCF parameter ${\mathit{c}}_{2}$=-0.007(3) is used. For ${\mathrm{Sm}}^{2+}$, however, the experimental results cannot be described by the same SCCF model. In fact, the pressure dependence of the splittings in the two multiplets $^{5}$${\mathit{D}}_{1}$ and $^{7}$${\mathit{F}}_{1}$ for ${\mathrm{Sm}}^{2+}$:BaFCl to ${\mathrm{Sm}}^{2+}$:CaFCl deviates extremely not only from the predictions of the conventional crystal-field models but also from the SCCF model, but these results are qualitatively explained when a significant configuration interaction between the 4${\mathit{f}}^{6}$ and 4${\mathit{f}}^{5}$5${\mathit{d}}^{1}$ configurations is taken into account. The present study shows that this 4f-5d configuration interaction results in very important contributions to correlation crystal fields for ${\mathrm{Sm}}^{2+}$ due to the close energetic proximity of these two configurations.