a magnetic tunnel junction having a first electrode separated from a second electrode by a tunneling barrier is provided . the tunneling barrier is a ferromagnetic insulator that provides a spin dependent barrier energy for tunneling . the first electrode includes a ferromagnetic , electrically conductive layer . electrons emitted from the first electrode toward the tunneling barrier are partially or completely spin - polarized according to the magnetization of the ferromagnetic electrode layer . the electrical resistance of the tunnel junction depends on the relative orientation of the electrode layer magnetization and the tunneling barrier magnetization . such tunnel junctions are widely applicable to spintronic devices , such as spin valves , magnetic tunnel junctions , spin switches , spin valve transistors , spin filters , and to spintronic applications such as magnetic recording , magnetic random access memory , ultrasensitive magnetic field sensing , spin injection and spin detection .