Electron spin injection and detection at a ferromagnetic-paramagnetic interface (invited)

Abstract

A new technique for investigating conduction electron magnetization is presented. A coupling between electronic charge and spin transport in ferromagnetic metals follows from generalizing the linear transport equations. In practice, this means that ferromagnetic films act as conduction electron spin polarizers. At an interface between a ferromagnetic and a paramagnetic metal, one can inject and detect nonequilibrium magnetization in the paramagnet, and use sensitive electric measurements to probe spin transport. Application of a small external magnetic field dephases the spins. The result is a new technique for measuring conduction spin relaxation times, which is demonstrated on bulk aluminum samples. Three advantages of the technique make it applicable to a wide range of studies. (1) The measurement can be made in the limit of zero field so that systems with interesting properties which are altered or destroyed by magnetic fields can now be probed (spin glasses, superconductors, metals with g anisotropies). (2) A SQUID voltmeter with picovolt noise floor provides a sensitivity that allows detection of one nonequilibrium spin in a background of 1012 equilibrium spins. (3) The experimental geometry utilizes microfabrication techniques and is ideal for application to small-size systems that are inaccessible to conventional electron spin resonance methods. The geometry conveniently needs but one good surface; other sample surfaces are available for alteration in situ for the study of surface relaxation effects. Finally, there are obvious applications to the study of ferromagnets and interfaces.