Stripe order in highly doped La_2-xSr_xNiO₄

Stripe order in La_2-xSr_xNiO₄ with 0.289 ≲ × ≲ 1/2 was studied with the neutron-diffraction technique. The stripe order of holes and spins was observed at low temperatures in all samples. The incommensurability ε of the stripe order is approximately linear with the hole concentration n_h up to x = 1/2. We found that the stripe is most stable at n_h = 1/3 with ε = 1/3 from the analyses of the onset temperatures of the charge and spin orderings and the n_h dependence of the correlation length of the stripe order. The stability of an ε = 1/3 stripe induces a systematic deviation of ε from the ε = n_h law for samples with n_h ≠ 1/3. This deviation affects the stripe order on both sides of the hole concentration with n_h < 1/3 as well as n_h > 1/3.