Magnetization of La2-xSrxNiO4+delta (0 <= x <= 0.5): Spin-glass and memory effects

We have studied the magnetization of a series of spin-charge-ordered La2-xSrxNiO4+delta single crystals with 0 <= x <= 0.5. For fields applied parallel to the ab plane there is a large irreversibility below a temperature T(F1)similar to 50 K and a smaller irreversibility that persists up to near the charge-ordering temperature. We observed memory effects in the thermoremnant magnetization across the entire doping range. We found that these materials retain a memory of the temperature at which an external field was removed and that there is a pronounced increase in the thermoremnant magnetization when the system is warmed through a spin reorientation transition.