Emergent inductance in ferromagnetic nanostructures

Several embodiments of emergent inductance in ferromagnetic nanostructures are theoretically presented. The emergent inductance is a universal phenomenon when an order parameter such as magnetization in ferromagnets is coupled with conduction electron spin based on a sequential action of spin torque and spinmotive force effects under ac current application. An original version of the emergent inductor using a spiral magnet can be extended to include the spin-orbit coupling effects. Materials are not limited to metallic systems but also insulators. A striking common feature over the emergent inductors is their size dependence of the effect; the inductance is inversely proportional to the sample cross sectional area, opening a way for integration of an inductor element. We also discuss key performance factors: the operation frequency and quality factor that represents the energy efficiency of the inductive response.