Large domain wall velocities in Pt/Co/GdOx and Pt/Co/Gd trilayers

We have carried out measurements of the velocities of magnetic domain walls (DW) driven by magnetic field pulses in symmetric Pt/Co/Pt and asymmetric Pt/Co/GdOx and Pt/Co/Gd trilayers [1]. The thickness of the Co layers was 0.8 – 1.0 nm, and in all layers the easy magnetization axis was perpendicular to the film plane. The maximum observed velocity is about 60 m/s in the symmetric trilayer, while it is 5 to 10 times higher in the asymmetric ones. This can be explained by the effect of the interfacial Dzyaloshinskii-Moriya interaction (DMI) in the asymmetric layers, leading to chiral Néel domain walls [2] which are much more stable than the Bloch domain walls present in the symmetric trilayer. The maximum observed DW speed scales as D/Ms, where D is the strength of the DMI and Ms the spontaneous magnetization. In Pt/Co/Gd, where the anti-parallel coupling between the magnetic moments of Gd and Co leads to a decrease of the total magnetisation as shown by X-ray Magnetic Circular Dichroism and Vibrating Sample Magnetometer measurements, very large DW speeds (up to 700m/s) are obtained.

Velocity_vs_Bz

References : [1] Thai Ha Pham, J. Vogel, J. Sampaio, M. Vanatka, J.-C. Rojas-Sanchez, M. Bonfim, D. S. Chaves, F. Choueikani, P. Ohresser, E. Otero, A. Thiaville and S. Pizzini, EPL (Europhysics Letters) 113, 67001 (2016). [2] A. Thiaville, S ; Rohart, E. Jué, V. Cros and A. Fert, EPL (Europhysics Letters) 100, 57002 (2012).

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