Eur. Phys. J. B (2013) 86: 86
https://doi.org/10.1140/epjb/e2012-30674-0

Regular Article

The role of disorder in the domain wall dynamics of magnetic nanostrips^*

¹ Department of Electrical Energy, Systems and Automation, Ghent University, 9000 Ghent, Belgium
² COMP Centre of Excellence, Department of Applied Physics, Aalto University, P.O. Box 14100, 00076 Aalto, Finland
³ ISI Foundation, Via Alassio 11/c, 10126 Torino, Italy
⁴ Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, 10135 Torino, Italy

^a e-mail: ben.vandewiele@ugent.be
^b e-mail: lasse.laurson@aalto.fi
^c e-mail: g.durin@inrim.it

Received: 24 July 2012
Received in final form: 23 November 2012
Published online: 6 March 2013

Abstract

We study the role of the disorder in the dynamics of the domain walls (DW) in nanostrips with in-plane magnetization. In contrast with previous works where the disorder is due to edge roughness, we consider the role of a random distribution of voids, thus simulating local changes of the magnetization saturation value. By making use of the high-speed computational capability of GPUs, and an ad hoc micromagnetic code, we compute the speed of DWs under both applied fields (up to 15 mT), and spin-polarized currents (up to 30 A/μm²), for four different void densities. Field and currents are applied for 20 ns. We also consider both adiabatic and non-adiabatic spin-torque effects (ξ parameter equal 0 and 0.04, respectively). For all the cases, we repeat the simulation for 50 realizations of the void distributions. No thermal effects are considered. While some results can be understood in the line of the models reported in the literature, some others are much more peculiar. For instance, we expect a lower value of the maximum DW speed. This actually occurs in the field driven case, but with a less dramatic drop at the Walker breakdown, due to the difficulty to nucleate an antivortex DW. When nucleated, it gets easily pinned, thus preventing its retrograde motion typical for disorder-free strips. In the case of current drive with non-adiabatic spin-transfer torque, the Walker breakdown current increases strongly with the void density. This results in an increased value of the maximum speed available. Another important consequence of the disorder is that at low fields/currents the depinning transition regions appear to be more rounded, resembling creep behavior. This can have important consequences in the interpretation of experimental data.