Charge correlations in cobaltates La2–xSrx CoO4

Abstract

We report on an elastic neutron scattering study of the charge correlations in La2–xSrx CoO4 with x = 1/3, 0.4 and 0.5. We found that the checkerboard charge ordering correlations present in the x = 0.5 sample persist in the x = 0.4 and 1/3 materials. These checkerboard charge ordering correlations are robust and explain the occurrence of nano‐phase separation in layered cobaltates for Sr‐concentrations away from half‐doping. The half‐integer reflections then arise from the nanometer‐sized hole‐rich regions (blue areas in title figure) instead of the undoped ones (red areas in title figure). The appearance of nano‐phase separation is an important ingredient for understanding the formation of hour‐glass shaped magnetic excitation spectra in La2–xSrx CoO4. Nano‐phase separation in La2–xSrx CoO4 (schematically). Red areas: undoped La2CoO4 islands, blue areas: checkerboard charge ordered regions; black, green and blue balls represent nonmagnetic Co3+ ions, magnetic Co2+ ions and oxygen ions, respectively; green arrows indicate Co2+ spins [1, 2].magnified imageNano‐phase separation in La2–xSrx CoO4 (schematically). Red areas: undoped La2CoO4 islands, blue areas: checkerboard charge ordered regions; black, green and blue balls represent nonmagnetic Co3+ ions, magnetic Co2+ ions and oxygen ions, respectively; green arrows indicate Co2+ spins [1, 2].(© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)