Creating Advanced Memory Devices Through Antiferromagnetic Materials

April 24, 2020 by Luke James

Researchers in Tokyo have reportedly managed to demonstrate a method that switches a novel material between two different non-volatile states at high speeds and accuracy.

In 1929, Hermann Weyl noticed that the newly derived Dirac equation implied the existence of a massless particle. This later became known as the Weyl fermion and was once believed to be the electrically neutral neutrino, a fermion with a mass that is much smaller than the other known elementary particles and interacts only via the weak subatomic force and gravity.

Almost 100 years later, in 2015, the Weyl fermion was discovered in reality and scientists have been trying to find uses for it ever since. Now, a research team at the University of Tokyo, led by Professor Satoru Nakatsuji are said to have discovered a way to use Weyl fermions to make advanced memory devices

"For a while now, ferromagnetic materials, magnets that behave in a familiar way, have been used to explore spintronic phenomena. But there is a better class of magnetic materials for this purpose called antiferromagnetic materials, which seem harder to work with but have many advantages,” said Tomoya Higo, a research associate. 


A diagram showing how Weyl points are controlled.

A diagram showing how Weyl points are controlled. Image credited to Higo et al

Antiferromagnetic Materials and Their Link to Memory Devices  

Antiferromagnetic materials are currently the subject of great interest from physicists and engineers because they feature many of the same useful properties of ferromagnetic materials. Who are also often subject to external magnetic fields due to the unique arrangement of their constituent parts.

When using them in memory devices, their accurate and robust properties are especially beneficial, but due to this unique arrangement, it is not fully known whether the antiferromagnetic state can be controlled with a simple electrical pulse as ferromagnetic states can. 


The Discovery of the Spin-Orbit Torque Switching Method

This is where the Weyl fermions come in, explains Hanshen Tsai, another research associate. In their sample material, antiferromagnetic manganese-tin alloy, Weyl fermions are found at Weyl points in momentum space.

These points have two states that could represent binary digits, and the researchers found that they can switch these states at a Weyl point by using an external electrical current applied to neighboring thin layers of this alloy and either platinum or tungsten. They named this method “spin-orbit torque switching”. 

According to the research team, this discovery could indicate that the massless Weyl fermion has been found in their antiferromagnetic material and that it can be electrically manipulated, potentially paving the way for the development of advanced memory devices that use this and similar materials.