Unusual slow magnetic relaxation on a SmCo₂/GdCo₂ domain wall junction at low temperature

The slow dynamics of the magnetization of a domain wall junction (ferromagnetic layers separated by an artificial planar barrier) has been studied through after-effect measurements. We show that two different dynamical magnetic processes take place at low temperature. The time and the thermal dependences of the magnetization suggest that a simple interpretation in terms of thermal activated processes is not always valid. An interpretation in terms of linear response to a local field is proposed.