Skyrmion production on demand by homogeneous DC currents

Topological magnetic textures -- skyrmions -- have become a major player in the design of next-generation magnetic storage technology due to their stability and the control of their motion by ultra-low current densities. A major challenge to achieve this new skyrmion-based technology is the controlled and systematic creation of magnetic skyrmions without the need of complex setups. We demonstrate a solution to this challenge by showing how to create skyrmions and other magnetic textures in ferromagnetic thin films by means of a homogeneous DC current and without requiring any standard "twisting" interactions like Dzyaloshinskii-Moriya. This is possible by exploiting a dynamical instability arising by the interplay of current-induced spin-transfer torque and locally engineered anisotropies. The magnetic textures are created controllably, efficiently, and periodically with a period that can be tuned by the applied current strength. We propose specific experimental setups realizable with simple materials, such as cobalt or permalloy, to observe the periodic formation of skyrmions. Thus our findings allows for the production of skyrmions on demand in simple ferromagnets by homogeneous DC currents.