X-Ray Scattering Studies Of Charge Stripes In Manganites And Nickelates

Single crystals of both (Bi0.24Ca0.76)MnO3 and (La1.67Sr0.33)NiO4 have been studied extensively using both laboratory and synchrotron radiation x-ray scattering. Using x-ray techniques, we have detected directly the formation of charge stripes. Weak satellite peaks with a modulation wave-vector q approximate to (0.25, 0.25, 0) were observed below the transition temperature in the perovskite (Bi0.24Ca0.76)MnO3 Measurements of the temperature dependence of the intensity and width of the charge-ordering satellites over the temperature range 10-240 K demonstrate that the correlation length of the charge-order stripes is long range at all temperatures and in all directions. A first-order structural phase transition accompanying the charge ordering was also studied. We also undertook SR x-ray measurements on (La1.67Sr0.33)NiO4, and found quasi-2D-fike charge stripes with a modulation wave-vector q approximate to (2/3, 2/3, 1). Detailed critical scattering measurements of the melting of the charge stripes gave critical exponents compatible with those expected of a 2D-Ising system.