Paramagnetic critical scattering

Fig. 6. Paramagnetic critical scattering in La2Cu04. Energy-integrating scans across the two-dimensional rod of scattering measure the Fourier transform of the instantaneous spin-spin correlation function in La2Cu04 above T. The peak width (corrected for finite instrumental resolution) is the inverse correlation length for antiferromagnetic spin fluctuations. The dashed lines show the experimental resolution function, and the solid lines are the results of fits to a Lorentzian lineshape convolved with the resolution for three different temperatures. From Kcimer et al. (1992).

Order of the Paramagnetic-Antiferromagnetic Transition. A second-order transition is indicated by various studies with neutrons, Ott, Kjems [14], and the behavior of thermal expansion and heat capacity around the N6el temperature [5].The temperature dependence of critical scattering definitely excludes the existence of a smeared-out first-order phase transition [14]. How-... 

Fig. 5. Upper critical field H 2 vs temperature for the compound YbBa2Cu307 j,. The solid lines are based on standard WHH (Werthamer et al. 1966) theory for a conventional type II superconductor in the limits of maximum (spin-orbit scattering parameter As = 0) and minimum (A5 =oo) paramagnetic limitation and have been fitted to the data near T. Inset Normalized electrical resistivity vs temperature in several magnetic fields between 0 and 9 tesla. From Markert et al. (1989a).

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