Skyrmion dynamics, nucleation, and stability in ferromagnetic thin film multilayers

Magnetic skyrmions are particle-like spin textures that are topologically protected from being continuously ‘unwound’. Recent work has shown that in transition metal based multilayers, isolated ordered skyrmion lattices and isolated skyrmions with size <50nm can be achieved at room temperature, with current-driven velocities exceeding 100m/s [1]. This talk focuses on recent developments in stabilizing, manipulating, and designing skyrmions in thin-film heterostructures. We first describe current-driven dynamics and nucleation driven by spin-orbit torques. Using pump-probe dynamic imaging, we demonstrate an analogue to the conventional Hall effect, in which the skyrmion trajectory depends on its topological charge much as a particle in a magnetic field is deflected due to its electric charge [2]. We then demonstrate deterministic current-induced skyrmion writing at sub-nanosecond timescales through the combined action of DMI and spin-orbit torque [3], and show that thermal excitation can drive morphological phase transitions between chiral phases in a controlled way [4]. We next present an analytical framework [5] for computing the energy and structure of any skyrmion in any material, which gives insight into skyrmion stability, allows for mapping the full materials parameter space, and provides a means to solve the inverse problem of designing skyrmions with desired properties through informed materials selection. Finally, we apply this framework to experimentally demonstrate ultrafast and ultrasmall skyrmions at room temperature, with sizes down to 10 nm, in appropriately engineered materials.

[1] S, Woo, et al. Nat, Mater. 15, 501 (2016)
[2] K. Litzius, et al., Nat. Phys. 13, 170 (2017)
[3] F. Büttner, et al., Nat. Nano. 12, 1040 (2017)
[4] I. Lemesh, et al., submitted (2017)
[5] F. Büttner, et al., submitted (2017); arXiv:1704.08489