A reversible system flips the magnetic orientation of particles using a small voltage. This could allow for faster data storage and smaller sensors.
Most magnets we see daily are made from “ferromagnetic” material. These materials have strong magnetism because the north-south magnetic directions of most atoms are aligned in the same direction. These materials are the foundation of most data storage devices used in high-tech today.
Magnets made from ferrimagnetic materials are rare. They are marked with an “I,” and some atoms are aligned one way, while others are in the opposite direction. The balance between these two types of magnets will determine the overall magnetic field they produce. If more atoms point in one order, this difference will create a net magnetic force in that direction.
Because their magnetic properties are strongly affected by external forces, ferrimagnetic material should be able to produce data storage and logic circuits faster than conventional ferromagnets. There has not been a reliable, simple, and fast way to change the orientation of these magnets to make them flip from a 0 into a 1.
This method was developed by researchers at MIT and other universities. It allows the ferrimagnet’s magnetic polarity to be rapidly switched 180 degrees using a minimal applied voltage. Researchers believe this discovery could lead to a new era in ferrimagnetic logic and data storage devices.
These findings are published in the journal Nature Nanotechnology in a paper written by Mantao Huang (MIT professor of materials science technology Geoffrey Beach) and Bilge Yildiz (MIT professor of nuclear science technology Bilge Yildiz), along with 15 other researchers from MIT, Germany, Spain, and Korea.
Gadolinium cobalt is a material that forms part of the rare earth transition metal ferrimagnets class. It is made up of two elements that form interlocking lattice atoms. The gadolinium and cobalt atoms preferentially have magnetic axes in one direction, while the cobalt ones point in the other. The balance of the two elements in its alloy composition determines the material’s overall magnetization.
Researchers discovered that oxygen could be vented if you use a voltage to separate water molecules from the film’s surface. At the same time, hydrogen atoms (or, more precisely, their single protons nuclei) can penetrate deep into the material and alter the balance of magnetic orientations. This change can flip the net magnetic field direction 180 degrees. This is precisely what is required for devices like magnetic memories.
Huang says adding hydrogen to the structure can significantly reduce gadolinium’s magnet moment. Magnetic moment refers to the strength of the field generated by an atom’s spin alignment.
Beach, co-director of MIT’s Materials Research Laboratory, said that the process is highly energy efficient because it involves a voltage change and not an applied electric current, which would cause heating and therefore waste energy through heat dissipation.
He says that injecting hydrogen nuclei into a material is straightforward. You would expect that if you took some fabric and put some atoms or ions in it, it would expand and crack. It turns out that these films are made of the proton, which is a tiny entity that can penetrate the bulk of the material without causing structural fatigue that could lead to failure.
The material’s stability was proven through rigorous tests. Huang claims that the material was tested with 10,000 polarity reverses without any signs of degradation.
Beach claims that the material also has other properties that could be useful. He explains that the magnetic alignment between individual atoms of the material acts a little like springs. This spring-like force pulls back if it moves out of alignment with others. When objects are connected by springs, they can generate waves that travel along the material. These are spin waves for magnetic materials. These oscillations can be caused by magnetization, and they can have extremely high frequencies.
He says that they can oscillate in the terahertz region, making them unique in their ability to generate or sense high-frequency electromagnetic radiation. This is something that only a few materials can do.
Beach said that sensors could be used to demonstrate the phenomenon in a matter of years. However, more complicated applications such as data and logic circuits may take longer due to the relative newness of ferrimagnet technology.
He says the primary method could also be used for other purposes beyond specific magnetic applications. He explains that this is a method to alter the properties of bulk materials by creating an electric field. He says, “That is an amazing feat in itself.” At the same time, other work has been done to control surface properties with applied voltages. However, the hydrogen-pumping method allows profound alteration that allows for “control of a wide range of properties.”
“Voltage-controlled flipping has been seeking to lower the power consumption of the spin device, which is the core mechanism of modern Silicon Technology,” Hyunsoo Yang (a professor of electrical engineering at the National University of Singapore), who was not involved in this study. He adds that the work used the voltage control concept to create a ferrimagnet that toggled the dominant sublattice. This resulted in magnetic bit writing. He believes this new method could “potentially revolutionize” the field if the required voltage can be decreased and the speed can be improved.
