Hybrid chiral domain walls and skyrmions in magnetic multilayers

Aiming at reducing the radius of individual magnetic skyrmions below 10 nm without making compromises between room-temperature stability and current-induced mobility¹, a multilayered magnetic system is often privileged². However, dipolar interactions can overcome the essential chiral properties of magnetic skyrmions stemming from the Dzyaloshinskii-Moriya interaction (DMI), for multilayers with too large magnetization or number of layers. Using circular dichroism in X-ray Resonant Magnetic Scattering, we demonstrate a reorientation of chirality along the vertical direction of magnetic domain-walls and skyrmions, leading to the formation of hybrid chiral skyrmions³. We next establish an extensive micromagnetic model of magnetic skyrmions, which allows obtaining their equilibrium profiles with an accurate and layer-resolved description of both size and chirality⁴. The resulting magnetization profiles allow predicting, within the Thiele formalism, the expected velocity of skyrmions under current-induced spin-orbit torques in different spin injection geometries. We find the requirements on the DMI magnitude to ensure an efficient motion, and observe a regime of compensation of the skyrmion Hall effect for hybrid chiral skyrmions. Beyond such issues related to the chirality of ferromagnetic skyrmions, we finally present our recent progresses in the study of multilayers hosting synthetic antiferromagnetic skyrmions, whose alternation of polarity enables a way to circumvent all issues related to dipolar interactions in skyrmion multilayers.
¹ F. Büttner et al, Sci Rep 8, 4464 (2018)
² C. Moreau-Luchaire et al, Nat Nano 11, 444 (2016); S. Woo et al, Nat Mater 15, 501 (2016)
³ W. Legrand et al, Sci Adv 4, eaat0415 (2018); Y. Dovzhenko et al, Nat Comm, 9, 2712 (2018)
⁴ W. Legrand et al, arXiv:1807.04935 (2018).