Direct observation of skyrmions by Lorentz TEM and evaluation of SOT efficiency in Pt/Gd/Co/Ni laminated systems

Skyrmions, topologically protected quasiparticles, exhibit novel physical properties, such as the topological Hall effect and emergent electromagnetic dynamics, making them highly promising for spintronic applications. Their small size combined with fast transport at low power makes them attractive candidates for next-generation information carrier. However, these advantages cannot currently be realized simultaneously. One potential solution involves enhancing the spin–orbit torque (SOT) transferred from the heavy metal Pt layer to the magnetic layer. Here, we control the SOT efficiency by inserting an ultrathin layer between Pt and Co, as prior studies suggest that such an insertion layer can increase the spin-mixing conductance, thereby modulating the SOT efficiency. However, the insertion layer may also reduce the interfacial Dzyaloshinskii–Moriya interaction, a key factor in stabilizing skyrmions. In this work, we evaluated the SOT efficiency and skyrmion stability for two samples, the Pt/Co/Ni/Pt and Pt/Gd/Co/Ni/Pt systems, using Lorentz transmission electron microscopy. No significant difference was observed between the two samples, indicating that the SOT efficiency remained unaffected by the Gd insertion, and skyrmions formed in both cases.