Muon-spin-relaxation studies of magnetic order in heavily doped La2-xSrxNiO4+delta

We report muon-spin-relaxation measurements on a series of compounds with composition La2-xSrxNiO4+delta where the net hole concentration x + 2 delta is greater than 0.4. A magnetic transition is found in all the samples studied which occurs at a composition-dependent temperature T-M. Below T-M clear precession signals are observed in zero applied magnetic field, indicating the existence of at least short-range magnetic order on a time scale greater than 10(-8) s. Above T-M the correlation times decrease by several orders of magnitude. The measurements of T-M as a function of the net hole concentration extend the determination of Neel temperatures by previous neutron diffraction measurements to higher doping levels.