Spin pumping is a method of generating a spin current, the spintronic analog of a battery in conventional electronics. In order to make a spintronic device, the primary requirement is to have a system that: can generate a current of spin-polarized electrons and is sensitive to the spin polarization. Most spintronic devices also have a unit in between these two that changes the current of electrons depending on the spin states. Candidates for such devices include injection schemes based on magnetic semiconductors and ferromagnetic metals, ferromagnetic resonance devices , and a variety of spin-dependent pumps. Optical, microwave and electrical methods are also being explored. These devices could be used for low-power data transmission in spintronic devices or to transmit electrical signals through insulators. Tunneling Spin tunneling transport at the interface between a normal metal and a ferromagnetic insulator can be driven by microwave irradiation on the ferromagnetic side. Magnetic Moment The spin pumped into an adjacent layer by a precessing magnetic moment is given by where is the spin current (the vector indicates the orientation of the spin, not the direction of the current), is the spin-mixing conductance, is the saturation magnetization, and is the time-dependent orientation of the moment. References See also Spintronic Spin wave Spin Engineering Spin Hall effect Spin memory loss Spintronics