Zero-Field Skyrmions in Confined Pt/Co/Ta Multilayer Nanodisks for Spintronic Devices

Magnetic skyrmions in heavy-metal/ferromagnet multilayers are promising building blocks for low-power spintronic devices; however, achieving thermally robust and field-free stability at room temperature remains a key challenge. Here, we present a combined experimental and micromagnetic investigation of confined skyrmions in Pt/Co/Ta multilayer nanodisks, with diameters ranging from 200 to 1000 nm, focusing on their switching behavior and numerical layer-resolved topological properties. Using polar magneto-optical Kerr effect, magnetic force microscopy, and micromagnetic simulations based on experimentally determined magnetic parameters, we show that lateral confinement strongly governs magnetization reversal and skyrmion stability. While continuous films exhibit labyrinthine stripe domains due to competing interfacial Dzyaloshinskii–Moriya interaction, exchange, and dipolar energies, nanodisks display pronounced size-dependent behavior: large disks remain multidomain, intermediate sizes favor skyrmion-mediated reversal, and sub-250 nm disks approach single-domain states. Notably, 400 nm nanodisks stabilize isolated Néel-type skyrmions at zero magnetic field and room temperature. Simulations reproduce the experimental hysteresis and reveal that confinement lowers the demagnetizing energy, stabilizing the skyrmion state. Layer-resolved topological analysis further uncovers two distinct remanent three-dimensional skyrmion configurations, selectable via modest fields (∼60 mT), with different chirality profiles and total topological charge. This controllable bistability provides a natural binary encoding scheme and, in a magnetic tunnel junction geometry, would enable nonvolatile memory operation through distinct resistance states.