Spin-dependent tunneling in magnetic junctions

This chapter reviews the physics of spin-dependent tunneling in magnetic tunnel junctions, i.e. ferromagnetic layers separated by an ultrathin, insulating barrier. In magnetic junctions the tunneling current between the ferromagnetic electrodes depends strongly on an external magnetic field, facilitating a wealth of applications in the field of magnetic media and storage. After a short introduction on the background and elementary principles of magnetoresistance and tunneling spin polarization in magnetic tunnel junctions, the basic magnetic and transport phenomena are discussed emphasizing the critical role of the preparation and properties of (mostly Al2O3) tunneling barriers. Next, key ingredients to understand tunneling spin polarization are introduced in relation to experiments using superconducting probe layers. This is followed by discussing a number of crucial results directly addressing the physics of spin tunneling, including the role of the polarization of the ferromagnetic electrodes, the interfaces between barrier and electrodes and quantum-well formation, and the successful use of alternative crystalline barriers such as SrTiO3 and MgO