Spin torque is a phenomenon in the field of physics that involves the transfer of angular momentum associated with the intrinsic spin of electrons in a material. It plays a crucial role in various applications related to electronics and information storage, particularly in the field of spintronics.
In traditional electronics, the movement of charge carriers (typically electrons) is used to transmit and process information. However, in spintronics, both the charge and the intrinsic spin of electrons are utilized to encode and manipulate information. The concept of spin torque is central to the operation of several spintronic devices.
Spin torque can be divided into two main components: the "current-induced torque" and the "spin-transfer torque."
Current-Induced Torque (STT, Spin Transfer Torque):
When a current of electrons flows through a material, their spins are aligned due to the interaction with their neighboring spins and the crystalline structure of the material. In ferromagnetic materials, where the electron spins tend to align parallel to each other, a flowing current can transfer angular momentum to the magnetic moments (spins) of the material's atoms. This transfer of angular momentum can influence the direction of the magnetic moments and, consequently, the magnetization of the material. This effect is known as the "current-induced torque" or "spin transfer torque."
The current-induced torque has applications in various spintronic devices, including magnetic tunnel junctions (MTJs), which are fundamental components in magnetic random-access memory (MRAM) technology. In MRAM, information is stored as the orientation of magnetic moments, and the spin torque effect helps read and write this information by manipulating the magnetization of the memory cells.
Spin-Orbit Torque (SOT):
Another aspect of spin torque involves the coupling of electron spin with its orbital motion (motion around the nucleus), which is referred to as "spin-orbit coupling." When an electric field is applied perpendicular to the direction of electron motion, it generates a "spin-orbit torque" that can influence the magnetization direction. This effect has applications in devices like spin Hall effect-based devices and topological insulators.
In summary, spin torque is a fundamental concept in the realm of spintronics, allowing for the manipulation of electron spins and their associated angular momentum to control the magnetic properties of materials. This phenomenon finds applications in various spintronic devices, such as MRAM, and is crucial for advancing technologies that rely on the efficient control and manipulation of magnetic moments and electron spins.