Two physical phenomena are understood to be at the origin of the spin-orbit torques (SOT): A bulk component, the Spin Hall Effect, and an interfacial component, commonly known as the Rashba Effect.
The Spin Hall effect induces a spin current transverse to the charge current flowing in the SOT layer, leading to a spin accumulation at the SOT interfaces, which then diffuses into magnetic materials.
The Rashba effect originates from the uncompensated electric field at the interface, resulting in an effective magnetic field directly acting on nearby magnetizations.
Both effects lead to magnetic torques, that can control the magnetization direction of an adjacent magnetic “storage” layer, to write a binary “0” or “1” in the MRAM cell.
SOT is based on spin-transfer effects, just as today’s STT MRAM. However, unlike STT, there is no need for a magnetic layer to spin-polarize the electrical current. The source of spins is simply the lattice of a SOT layer material via the spin-orbit interaction.
- SOT : Spin Orbit Torque - © Antaios 2021
