4. Spin-orbit effects

Both GMR and TMR are based on the injection of a spin current and its detection by ferromagnetic electrodes. Since 2000-2010, it has become apparent that spin manipulation can be achieved not only via the exchange interaction in a ferromagnetic material, but also using spin-orbit coupling. This coupling is a relativistic effect: when an electron subjected to an electric field moves at a quasi-relativistic speed, a magnetic field appears in the electron's frame of reference, which acts on the electron's spin via the Zeeman interaction. The degree of freedom corresponding to the electron's momentum, usually decoupled from the spin, here becomes coupled to the spin.

As a result, spin injection and detection are no longer limited to ferromagnetic materials, and by using materials and interfaces with strong spin-orbit coupling, it becomes possible to realize the conversion...