Creation of magnetic skyrmions by surface acoustic waves

Non-collinear and non-coplanar spin textures, such as chiral domain walls¹ and helical or triangular spin structures^2,3, bring about diverse functionalities. Among them, magnetic skyrmions, particle-like non-coplanar topological spin structures characterized by a non-zero integer topological charge called the skyrmion number (N_sk), have great potential for various spintronic applications, such as energy-saving, non-volatile memory and non-von Neumann devices^4-7. Current pulses can initiate skyrmion creation in thin-film samples^8-10 but require relatively large current densities, which probably causes Joule heating. Moreover, skyrmion creation is localized at a specific position in the film depending on the sample design. Here, we experimentally demonstrate an approach to skyrmion creation employing surface acoustic waves (SAWs); in asymmetric multilayers of Pt/Co/Ir, propagating SAWs induce skyrmions in a wide area of the magnetic film. Micromagnetic simulations reveal that inhomogeneous torque arising from both SAWs and thermal fluctuations creates magnetic textures, with pair structures consisting of a Néel skyrmion-like and an antiskyrmion-like structure. Subsequently, such pairs transform to a Néel skyrmion due to the instability of the antiskyrmion-like structure in a system with interfacial Dzyaloshinskii-Moriya interaction. Our findings provide a tool for efficient manipulation of topological spin objects without heat dissipation and over large areas, given that the propagation length of SAWs is of the order of millimetres.