Hole concentration dependence of the ordering process of the stripe order in La_2-xSr_xNiO₄

Ordering process of stripe order in La_2-xSr_xNiO₄ with x being around 1/3 was investigated by neutron-diffraction experiments. When the stripe order is formed at high temperature, incommensurability ε of the stripe order has a tendency to show the value close to 1/3 for the samples with x at both sides of 1/3. With decreasing temperature, however, ε becomes close to the value determined by the linear relation of ε=n_h, where n_h is a hole concentration. This variation of the ε strongly affects the character of the stripe order through the change of the carrier densities in stripes and antiferromagnetic domains.