ABSTRACT
This chapter introduces the basis for the tunneling magnetoresistance (TMR) effect and its characteristic dependencies, for instance, the dependence of the TMR and conductance on applied bias, temperature, and materials choice. TMR is a consequence of spin-dependent tunneling, and in a broader sense, another manifestation of spin-dependent transport related to the giant magnetoresistance and anisotropic magnetoresistance effects. The quantum mechanical tunnel effect is one of the oldest quantum phenomena, dating back to the late 1920s. The spin-polarized tunneling technique developed by Meservey and Tedrow utilizes a superconductor as one electrode in a tunneling device to probe the tunneling spin polarization of electrons in the counter-electrode within a few hundreds of μeV of the Fermi level. The dependence of tunneling current on the density of states, coupled with spin conservation during tunneling, makes it reasonable to anticipate that interesting spin-dependent tunneling effects may be observed without resorting to the use of a superconducting spin detector.
