Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

As three-dimensional nanomagnetism evolves, novel non-trivial magnetic textures emerge as appealing information carriers for spintronics based on curved nanosystems and particularly Cylindrical Nanowires (NWs) [1,2]. One of the most fascinating candidates that is likely to reach the high velocities required for fast recording technologies is the Bloch Point (BP) domain wall (DW). Recently, theoretical evidence indicated that BPs in NWs could reach high velocities close to 2 km/s in the magnonic regime [2]. While the observation of the BP DW in cylindrical NWs is no longer recent [2], scarce numerical studies that combine both spin-polarized current and Oersted field have been published in NWs [4,5], despite first attempts to measure DW velocities are in progress [6].
In this work we evaluate the dynamics of the BP DW under both current directions in a Ni NW with 100 nm in diameter. We investigate two cases: i) pre-nucleated BP DW, and ii) the BP DW formed from the transformation of a Vortex-Antivortex DW. Here the effects of both spin-polarized current and Oersted field are considered. We discuss in detail the role of the chirality of the BP in relation to the Oersted field, also reported previously in precursors of BPs [4].

Here we show that while the pre-nucleated DW with the same chirality as that of the Oersted field propagates always against the current direction, the BP originated either from the transformation of the BP with the opposite chirality or from the vortex-antivortex DW can either stop the propagation or propagate parallel to the current. Finally, we provide values of the velocities achieved by the BP in the NW as a function of applied current in Fig. 1.

We conclude that BPs with vanishing momentum propagate opposite to the current with velocities that may be suppressed by the Oersted field. Importantly for spintronic applications, momentum plays a major role in the dynamics of BPs that has not been envisaged up to know.

[1] A. Fernandez-Pacheco et al., Three-dimensional nanomagnetism. Nat Commun 8, 15756 (2017)
[2] S. Da Col et al., Observation of Bloch-point domain walls in cylindrical magnetic nanowires, Phys. Rev. B, 89, 180405 (2014).
[3] X.-P. Ma et al., Cherenkov-type three-dimensional breakdown behavior of the Bloch-point domain wall motion in the cylindrical nanowire, Appl. Phys. Lett. 117, 062402 (2020).
[4] J.A. Fernandez-Roldan et al., Electric current and field control of vortex structures in cylindrical magnetic nanowires, Phys. Rev. B 102, 024421 (2020).
[5] C. Bran et al, Magnetic Configurations in Modulated Cylindrical Nanowires, Nanomaterials 11, 600 (2021). DOI: 10.3390/nano11030600
[6] M. Schöbitz et al., Fast Domain Wall Motion Governed by Topology and Oersted Fields in Cylindrical Magnetic Nanowires. Phys. Rev. Lett. 123, 217201 (2019).