EPR investigation ofCu2+tetramers in ferroelectricCsH2PO4

EPR study of ${\mathrm{CsH}}_2$ ${\mathrm{PO}}_4$ (CDP) single crystals with 0.005 mol % of ${\mathrm{Cu}}^{2+}$ at room temperature reveals isolated ${\mathrm{Cu}}^{2+}$ (S=(1/2)) complexes with four ligand coordination and spin Hamiltonian parameters $g_{\mathrm{para}}$=2.2575, $g_{\perp }$=2.1866, $A_{\mathrm{para}}$=30 G, and $A_{\perp }$=27 G. At temperatures below 250 K the spectra were observed to have fine structure and are described as arising from a ${\mathrm{Cu}}^{2+}$ tetramer with effective spin S=2 and spin Hamiltonian parameters D=0.181 ${\mathrm{cm}}^{\mathrm{-}1}$, E=-0.081 ${\mathrm{cm}}^{\mathrm{-}1}$, a=0.001 ${\mathrm{cm}}^{\mathrm{-}1}$, b=0, and c=-0.021 ${\mathrm{cm}}^{\mathrm{-}1}$. Also reported are transitions within the S=1 multiplet of the tetramer, and a microscopic model of superexchange interaction has been used to evaluate the parameters $D_x$=0.543 ${\mathrm{cm}}^{\mathrm{-}1}$ and $E_x$=-0.159 ${\mathrm{cm}}^{\mathrm{-}1}$. A tetramer model as well as a temperature dependence of the ratio of tetramer–to–single-ion intensity is presented.