Magnetic Soft Actuators: Magnetic Soft Robots from Macro- to Nanoscale

In this chapter, we make the very first attempt to apply concepts of curvilinear magnetism to the active research field ofmagnetic soft actuators and, in particular, magnetic soft robots. Specifically, we describe the interplay between the mechanical and magnetic degrees of freedom in mechanically flexible materials. The discussion starts with the common approach based on the analysis of the balance of magnetic and mechanical forces and torques to describe the actuation behavior and performance of mechanically soft magnetic thin films, wires and ribbons. The framework of curvilinear magnetism is then applied to provide an intuitive physical picture of a complex behavior of actuators possessing a complex magnetic texture. This approach allows us to predict new effects with broken symmetry on bending and twisting of actuators. For instance, a selected handedness of the magnetization rotation within the magnetic texture can lead to the energetically preferable clockwise or counter-clockwise mechanical twist. Furthermore, the chapter covers the topic of mechanically extremely soft magnetic samples (spin chains and ribbons) where the magnetic texture can affect the shape of the actuator (enable permanent bends or twists) even without applied magnetic fields. These systems can be of use for prospective magnetic robotics at the nanoscale. In this respect, the magnetic texture can result in similar mechanical effects as typically realized using shape memory polymers. We hope that this chapter will stimulate active experimental research on the validation of these recent theoretical predictions and result in the development of new application scenarios, where the asymmetric motion of magnetic actuators is the key enabler.