Determination of incommensurate lattice modulations in La0.4Sr1.6MnO4 by resonant r-ray scattering

Abstract

Superlattice reflections, which appear below the semiconductor-insulator phase transition temperature in La0.4Sr1.6MnO4, have been investigated by Resonant X-ray Scattering. We have observed two types of resonant reflections with modulation wave vectors qh±epsilon = (h±epsilon, h±epsilon, 0) and qh±2epsilon = (h±2epsilon, h±2epsilon, 0) (h=integer, epsilon=0.2) in the I4/mmm setting. The energy dependence across the Mn K-edge, together with the azimuthal angle, polarization and temperature evolution have shown that reflections with 2epsilon periodicity only appear in the σ-σ' channel, involving resonant and non-resonant scattering. On the other hand, reflections with epsilon periodicity exclusively appear in the σ-π' channel on resonance and the scattered intensity follows a π-periodicity with the azimuthal angle. We demonstrate that this different behaviour discards any possible Mn3+-/Mn4+-like bimodal stripe ordering but it can be easily explained as due to oxygen displacements sinusoidal modulated along and perpendicular to the tetragonal [1, 1, 0] direction.