Publications by Colleges and Departments (MSU - Bozeman)
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Item Dielectric measurements of the proton-glass state in Rb0.65(NH4)0.35H2AsO4(1988-09) Trybuła, Z.; Schmidt, V. Hugo; Drumheller, John E.; He, Di; Li, ZhouningDielectric measurements of the Rb1−x/emph>(NH4)xH2AsO4 (x=0.35) mixed crystals in the a and c tetragonal directions in the temperature range from 3 to 300 K are reported. Below Tg a dielectric dispersion of ε’(T) and ε’’(T) in the applied frequency range from 1 Hz to 30 kHz was observed. A small anisotropy of the proton-glass transition temperature Tg was detected, but we did not find the large anisotropy reported by J. Kim, N. Kim, and K. Lee [J. Phys. C 21, L-663 (1988)].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.