ABSTRACT

Magnetic skyrmions are topological spin textures [1] that can be found in magnetic materials which break bulk or interface inversion symmetry, in which the skyrmions are stabilized by the Dzyaloshinskii-Moriya interaction (DMI) [2]. Due to their reduced size (as small as a few atomic lattices) and expected low depinning threshold for current-induced motion, magnetic skyrmions are expected to allow for improved scalability and be suitable for "abacus"-type applications in information and communication technologies [3].

Up to the last years, magnetic skyrmions were observed mostly at low temperature and under large magnetic fields in a few bulk non-centrosymmetric compounds and magnetic monolayers. In this talk, I will present experimental results at RT on small skyrmions (30-80 nm) in several types of multilayers associating magnetic layers of Co and nonmagnetic layers of heavy metals (Pt, Ir, Ru etc…) [4]. Then I will illustrate the wealth of skyrmions and will describe i) the creation of skyrmions by current pulses and its mechanism [5], ii) the detection of skyrmions (one by one) by Anomalous Hall Effect measurements [6], iii) the current-induced motion of skyrmions, the influence of defects on velocity and Skyrmion Hall Angle [5]. Finally, I will present results on shaping skyrmion profile and chirality in 3D [7] by a control of the relative values of DMI and dipole interactions for a given number of layers (experimentally determined by x-ray magnetic scattering, XRMS) and its impact on spin torque induced dynamics [8].

These advances made in technologically relevant materials opens the way for the development of several concepts of skyrmion based devices going from race-track memory type to MRAM, from still highly silicon-compatible memories, such as multi-level MRAM or skyrmion racetrack memories to disruptive "beyond CMOS" technologies such as neuro-inspired architectures.

Ackn: EU grant MAGicSky No. FET-Open-665095, FLAG-ERA SoGraph (ANR-15-GRFL-0005), ANR grant TOPSky (ANR-17-CE24-0025) and DARPA MIPR# HR0011831554.

References

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[1] A.N. Bogdanov & U.K. Rößler, Phys. Rev. Lett. 87, 037203 (2001); [2] N. Nagaosa, Y. Tokura, Nature Nanotech. 8, 899 (2013) ; [3] A. Fert, N. Reyren, V. Cros, Nat. Rev. Mat. 2, 17031 (2017); [4] C. Moreau-Luchaire, VC et al., Nat. Nanotech, 11, 444 (2016); [5] W. Legrand et al., Nano Letters 17, 2703 (2017); [6] D. Maccariello, VC et al., Nat. Nanotech. (2018); [7] J.Y. Chauleau, VC et al., Phys. Rev. Lett. 120, 037202 (2018); [8] W. Legrand, VC et al., Science Adv. (2018)