with $H_{x}$, which depends on the details of the Co/Gd interface. Since the measurements were taken with ms-long pulses in the creep regime and with ns-long pulses in the flow regime, the effect of the pulse length on the DW pinning may also play a role.

Some information on the nature of the top interface, as the presence or not of CoO, can be obtained from the temperature dependence of magnetic hysteresis loops. We have carried out magnetisation measurements with variable temperature between 10K and 300K in a VSM-SQUID of Quantum Design (Figure \[fig:VSM\]). For sample (C) a change of the hysteresis loops, which are square with 100% remanence at 300K, is observed around 225K, where they become partly tilted and the remanence decreases to about 60%. This indicates a decrease of the PMA. Upon decreasing the temperature further, the coercivity increases strongly and below 70K a shift of the hysteresis loop to negative fields develops. Both observations can be attributed to the presence of an ultrathin layer of CoO at the Co/Gd interface, which becomes antiferromagnetic around 225K with a blocking temperature around 70K. For sample (D), the only one presenting expected $v(H_{x}$) curves in the creep regime, the 