Using Spin Current to Write Data
Though flash-based SSDs may be replacing magnetic hard drives in many of our machines, the traditional HDD is still a common piece of computer hardware. The technology is approaching a limit however, as bits can only be so small before writing one bit risks disrupting those around it. Researchers at Eindhoven University of Technology have developed a more efficient way of writing magnetic bits though, that could increase speeds tremendously.
Typically flipping a bit requires a local magnetic field, causing the magnetic properties of the hard disk material to change from one state to another. The two states can be read as either zero or one, for binary data. Instead of using a magnetic field though, the Eindhoven researchers use ultrafast lasers to trigger a spin current. Spin is an intrinsic property of many particles, including electrons, and its direction determines the direction of the particle's magnetic field. A spin current is just a flow of electrons all with the same spin. To produce the current, the researchers fired ultrafast laser pulses at a material made of two magnetic layers, with a neutral layer in between. When the laser strikes the top layer, the electrons in it try to move through the material, and take with them the spin of the top later. This spin then exerts a force on the bottom layer, causing it to flip its magnetic state.
The changes in magnetic state of the bottom layer take around 100 femtoseconds, which is approximately 1000 times faster than modern technology can achieve. While that is definitely impressive for write speeds, because of the use of lasers, this technology could also be used in future optical computers, for data storage.