Strong Current Actions On Ferrimagnetic Domain Walls In The Creep Regime

We observe domain-wall (DW) motion in ferrimagnetic TbFe wires with perpendicular anisotropy under combined field and current in the creep regime. The current action on the DW is double: Joule heating and spin-transfer torque. We propose a genuinely robust analysis of velocity, separating thermal effects and spin-transfer torque, quantifying the latter as an equivalent field in the so-called one-dimensional (1D) model. Its efficiency is much larger than in transition-metal ferromagnets above room temperature. The equivalent field reveals the large polarization-to-magnetization ratio in ferrimagnets despite a vanishing Ms. The usual 1D DW model is extended to mimic creep and predicts that, in low net magnetization systems, the internal DW structure precesses with currents above a field-independent threshold, leading to two propagation regimes with different mobilities. This is another example of how the internal DW magnetization is relevant in creep. We could not detect experimentally these two regimes, possibly because of the dispersion of the data.