Incommensurate stripe order in La2-xSrxNiO4 with x=0.225

In recent studies of La2-xSrxNiO4 it has been suggested that ordering of the dopant-induced holes occurs only commensurately at special values of x, such as 1/3 and 1/2. Commensurate order of both charge and spin densities has also been found in a crystal with x = 0.20. The present neutron scattering study of an x = 0.225 crystal demonstrates that the spin and charge order can also be incommensurate. In fact, the incommensurability is temperature dependent, as observed previously in La2NiO4.125, indicating that such behavior is intrinsic to the doped NiO2 layers and not dependent on ordering of the dopant ions. A careful analysis of the unusual variation of peak widths as a function of momentum transfer perpendicular to the planes shows that the charge- and spin-density modulations are tied to the lattice, with the shift in phase of the charge modulations from one layer to the next equal to exactly one in-plane lattice spacing. A comparison of results for a number of samples shows that the charge and spin ordering temperatures vary linearly with hole concentration, with charge order always occurring at higher temperature, clearly indicating that the ordering is driven by the charge.