The emerging technology known as spintronics utilizes the spin of electrons to store and manipulate data, and promises devices that are quicker and more energy-efficient than conventional electronics. But a major obstacle holding this technology back has been figuring out how to effectively generate the spin current in the first place. Fortunately, scientists have recently formulated a new method for quickly creating currents using ultra short laser pulses.
The laser pulse hits nickel (green), exciting the electrons, which move towards the silicon (yellow), causing more spin up electrons (red) to pass into the silicon than spin down ones (blue). Image source: TU Wien.
Spintronics transport data via the angular momentum of electrons, or their spin, as opposed to electronic chips transporting data through electrical charges. With the spinning up or spinning down of the angular momentum of electrons, individual electrons are able to represent either of the two binary states.
Initial research efforts in the area of getting the spin current flowing was focused on the use of ferromagnetism. This was because a magnetic field is created when many electrons in a metal are spinning in the same way, so using ferromagnets to control how the electrons are spinning seemed like an obvious route to take.
“There have been attempts to send an electric current through a combination of magnets and semiconductors”, said Marco Battiato, one of the researchers working on the project at the University of Technology in Vienna, Austria. “The idea is to create a flux of electrons with uniform spin, which can then be used for spintronic circuits. But the efficiency of this method is very limited.”
Battiato and fellow scientist Karsten Held developed a new method for generating the spin current, which can be performed quickly. In computer simulations, the team attached a layer of nickel to silicon, and zapped the nickel with short laser pulses. This excited the electrons in the nickel, causing them to move towards the silicon, with some passing through into it. The key is that spin up electrons can move more freely in nickel than spin down ones, so the majority of those that reach the barrier and pass into the silicon are electrons with a spin up current. In doing this, the researchers have effectively injected silicon with a specific spin current, without creating an electrical charge.
“Spintronics has the potential to become a key technology of the next few decades”, said Battiato. “With our spin injection method there is now finally a way to create ultrafast, extremely strong spin currents.”
The team is currently working to bring the method to physical experiments.
Source: Physical Review Letters
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