In this paper we report studies of the charge stripe ordering using high resolution x-ray scattering in the nickelate system ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Ni}{\mathrm{O}}_4$ with doping levels of $x=0.33$, $x=0.30$, and $x=0.275$. The charge stripes for all doping levels were found to be two dimensional in nature with a high degree of correlation in the $a\text{−}b$ plane. The in-plane inverse correlation length in the lower doped systems was greater than that in the $x=0.33$ system and is greatest for $x=0.275$, consistent with the stripes becoming less correlated as the doping level is decreased from $x=0.33$. However, the charge ordering in the $x=0.33$ system was observed to be more two dimensional in nature with a greater inverse correlation length between planes. The interaction between the lattice and charge order was observed to stabilize the charge ordering, even in the absence of spin ordering. In the $x=0.30$ and $x=0.275$ systems no long-range charge order could exist without the presence of the magnetic order. In both systems the charge stripes were incommensurate and on heating the incommensurability increased towards the stable $\epsilon =0.33$ value as the stripes gained thermal energy to overcome the Coulombic repulsion. In all these systems the integrated intensity of the stripe reflections showed a clear difference in behavior from previous neutron studies with an initial increase in the integrated intensity as the temperature was increased, which was not found in the neutron studies.

• Received 26 April 2004

DOI:https://doi.org/10.1103/PhysRevB.70.144507