Room-temperature skyrmions have been presented as potential candidates for encoding information bits in several types of new spintronic devices 1. There have been many recent progresses allowing to stabilize sub-100 nm skyrmions at room temperature in crystalline ferromagnetic thick layers or in (amorphous) thin magnetic multilayers (MML) 2. In most case, at least in extended films or large structures, the application of relatively large perpendicular field (a few 10 mT) is needed which might be unfavorable for most of the anticipated skyrmion based devices. Hence, the stabilization of zero-field isolated skyrmions or skyrmion lattices is an important step towards application. There are recent works demonstrating isolated zero-field skyrmions stabilized due to interlayer exchange in polycrystalline 3, epitaxial 4 or exchange biased 5 trilayers. Here we demonstrate a new approach showing that room-temperature zero-field skyrmion lattices can be stabilized in MML. We develop a system in which perpendicular magnetic anisotropy, chiral order and bias field strength, through a non-magnetic spacer, can be adjusted simultaneously. Typical stacking sequence is schematically presented in Figure 1 (a). The samples have been characterized first by standard magnetometry (Fig. 1b). Relying on the interlayer electronic coupling to an adjacent bias magnetic layer with strong perpendicular magnetic anisotropy (uniform configuration), we demonstrate by Magnetic Force Microscopy that the remnant wormy-stripe “as-grown” domains (Fig. 1d) can be turned into skyrmion lattice phase (Fig. 1c). The skyrmion density and size can be modified by finely tuning the thicknesses of the layers allowing the control of the parameters related in the stabilization of the lattices. ANR TOPSKY (ANR-17-CE24-0025), DARPA TEE program (MIPR#HR0011831554) and EU SKYTOP (H2020 FET Proactive 824123) are acknowledged for financial support.

References
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