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Item EPR investigation of Cu2+ tetramers in ferroelectric CsH2PO4(1985-07) Waplak, S.; Schmidt, V. Hugo; Drumheller, John E.EPR study of CsH2PO4 (CDP) single crystals with 0.005 mol % of Cu2+ at room temperature reveals isolated Cu2+ (S=(1/2)) complexes with four ligand coordination and spin Hamiltonian parameters gpara=2.2575, g⊥=2.1866, Apara=30 G, and A⊥=27 G. At temperatures below 250 K the spectra were observed to have fine structure and are described as arising from a Cu2+ tetramer with effective spin S=2 and spin Hamiltonian parameters D=0.181 cm−1, E=-0.081 cm−1, a=0.001 cm−1, b=0, and c=-0.021 cm−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 Dx=0.543 cm−1 and Ex=-0.159 cm−1. A tetramer model as well as a temperature dependence of the ratio of tetramer–to–single-ion intensity is presented.Item EPR determination of three-dimensional correlations below the ferroelectric phase transition in pseudo-one-dimensional CsH2PO4:Cu2+(1986-11) Waplak, S.; Schmidt, V. Hugo; Drumheller, John E.The polarization fluctuations of ferroelectric CsH2PO4 above Tc are generally classified as a quasi-one-dimensional phenomenon. The temperature dependence of the EPR line splitting of the S=1 state of the Cu2+ tetramer, however, exhibits a critical exponent below Tc of β=0.5 indicating that the correlations associated with the order parameter are three dimensional below Tc.