Wave Vector Difference of Magnetic Bragg Reflections and Low Energy Magnetic Excitations in Charges-tripe Ordered La2NiO4.11

We report on the magnetism of charge-stripe ordered La2NiO4.11 +/- 0.01 by neutron scattering and mu SR. On going towards zero energy transfer there is an observed wave vector offset in the centring of the magnetic excitations and magnetic Bragg reflections, meaning the excitations cannot be described as Goldstone modes of the magnetic order. Weak transverse field mu SR measurements determine the magnetically order volume fraction is 87% from the two stripe twins, and the temperature evolution of the magnetic excitations is consistent with the low energy excitations coming from the magnetically ordered volume of the material. We will discuss how these results contrast with the proposed origin of a similar wave vector offset recently observed in a La-based cuprate, and possible origins of this effect in La2NiO4.11.