Stabilization and observation of zero-field skyrmions in ferromagnetic and synthetic antiferromagnetic systems*

Recently room-temperature skyrmions in ferromagnetic films and multilayers has been demonstrated and they show promise for encoding information bits in new computing technologies [1]. However, in ferromagnetic systems, the observation of skyrmions requires a substantial perpendicular field. Here we show that inserting a bias layer and utilizing interlayer electronic coupling, we successfully stabilize sub 100 nm skyrmions at zero field. A remaining challenge is that a transverse deflection of moving ferromagnetic skyrmions is present that hinder their efficient manipulation. Antiferromagnetic skyrmions could lift these limitations [4-5]. Here, we also show that room-temperature antiferromagnetic skyrmions can be stabilized in synthetic antiferromagnet (SAF) systems. Utilizing also a bias layer, we demonstrate by MFM [6] and by spin NV relaxometry [7] that the spin-spiral state obtained in a SAF system with vanishing perpendicular anisotropy can be turned into isolated antiferromagnetic skyrmions stable at zero field. These experimental results are completed with model-based estimations of their size and stability, showing that room-temperature stable antiferromagnetic skyrmions below 10 nm in radius can be anticipated in further optimized SAF systems [6]. Antiferromagnetic skyrmions in SAF systems may thus solve major issues associated to ferromagnetic skyrmions for low-power spintronic devices.
[1] A. Fert, N. Reyren, V. Cros, Nat. Rev. Mat. 2, 17031 (2017)
[2] C. Moreau-Luchaire et al., Nat. Nanotech. 11, 444 (2016)
[3] W. Legrand et al., Nano Letters 17, 2703 (2017)
[4] X. Zhang et al., Nat. Commun. 7, 10293 (2016)
[5] R. Tomasello et al, Scien. Rep. 4, 6784 (2014)
[6] W. Legrand et al, Nat. Materials 19, 34 (2020)
[7] A. Finco et al, arXiv:2006.13130