A new approach to controlling magnetism in a microchip could open doors to storage, computing and sensing devices that consume significantly less power than previous versions. The approach could also overcome some of the inherent physical limitations that have slowed down progress in this area.
Researchers at MIT and the Brookhaven National Laboratory have shown they can easily control the magnetic properties of a thin film material by applying a small voltage. The magnetic alignment changes thus made remain in their new state, unlike today's standard memory chips, without requiring a permanent power supply.
The new finding is published today in the journal Nature Materials in an article by Geoffrey Beach, Professor of Materials Science and Engineering and co-director of the MIT Materials Research Laboratory; PhD student Aik Jun Tan; and eight more at MIT and Brookhaven.
As silicon microchips reach fundamental physical limits that could limit their ability to further enhance their capabilities while reducing their energy consumption, researchers have been exploring a variety of new technologies including these Could bypass borders. One of the promising alternatives is an approach called spintronics, which uses the property of the electron called spin instead of its electric charge.
Because spintronic devices can maintain their magnetic properties without the need for a constant power that requires silicon memory chips, they require far less power to operate. They also generate far less heat ̵
However, Spintronic technology suffers from its own limitations. One of the major missing components was a way to easily and quickly control the magnetic properties of a material by applying a voltage. Many research groups around the world have been following this challenge.
Previous attempts have been based on the accumulation of electrons at the interface between a metallic magnet and an insulator using a device structure similar to a capacitor. The electrical charge can change the magnetic properties of the material, but only by a very small amount, making it impractical for use in real equipment. It has also been attempted to use ions instead of electrons to alter the magnetic properties. For example, oxygen ions have been used to oxidize a thin layer of magnetic material, causing extremely large changes in magnetic properties. By introducing and removing oxygen ions, the material swells and shrinks, causing mechanical damage that limits the process to a few repetitions – making it practically useless for computing devices.
The new finding shows a way out by using hydrogen ions instead of the much larger oxygen ions used in earlier experiments. Because the hydrogen ions are very easy to put on and take off, the new system is much faster and offers further significant benefits, the researchers said.
Since the hydrogen ions are so much smaller, they can enter and exit the crystalline structure of hydrogen ions. The spintronic device always changes its magnetic alignment without damaging the material. In fact, the team has now shown that after more than 2,000 cycles, the process does not cause material degradation. And unlike oxygen ions, hydrogen can easily penetrate metal layers, allowing the team to control the properties of layers deep in a device that could not be controlled in any other way.
"When you pump hydrogen toward the magnet, the magnetization is spinning," says Tan. "You can actually switch the direction of magnetization by 90 degrees by applying a voltage – and it is completely reversible." Since the orientation of the poles of the magnet is used to store information, you can simply write and write with this effect Data bits in Spintronic devices.
Beach, whose laboratory discovered the original process of controlling oxygen-ion magnetism a few years ago, says that initial evidence has triggered broad-based research into a new area called "magnetic ions". and now this latest insight has "turned this whole field upside down."
"This is truly a major breakthrough," says Chris Leighton, Distinguished McKnight University Professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota, who was not involved in this work. "Currently, there is great worldwide interest in controlling magnetic materials simply by applying electrical voltages. Not only is it interesting from a fundamental point of view, but it is also a potential game changer for applications that use magnetic materials to store and process digital information. "
Leighton says," Using hydrogen to control magnetism is not new. But doing this in a voltage controlled manner in a semiconductor device with good effects on the magnetic properties – that's pretty significant! He adds, "This is something new, with the potential to open up new research areas in addition. … At the end of the day, controlling every kind of material function by literally flipping a switch is quite exciting. Being able to do this fast enough and over enough cycles would be a fantastic advance for science and technology. "
In essence, according to Beach, he and his team attempt" a magnetic analogue of a transistor "that can be repeatedly turned on and off without affecting its physical properties.
Just add Adding Water
The discovery came about in part by accident, and while experimenting with layered magnetic materials in search of ways to change their magnetic behavior, Tan found that the results of his experiments were very day-to-day for obvious reasons When he finally examined all the conditions during the various tests, he found that the main difference was in the humidity: the experiment worked better on wet days than on dry ones, finally he realized that water molecules from the air on the charged surface of the material split into oxygen and hydrogen While the oxygen could escape into the air, the hydrogen was ionized and penetrated into the magnetic device – and changing its magnetism.
The team-made device consists of a sandwich of several thin layers, including a cobalt layer, in which the magnetic changes take place between layers of a metal like palladium or platinum and between two layers, a superposition of gadolinium oxide and then a gold layer to connect the electrical voltage.
The magnetism is switched over with only a brief application of voltage and then stops. No power is required for the inversion, only the device needs to be shorted to electrically connect its two sides, whereas a conventional memory chip requires constant power to maintain its state. "Because you only use one pulse, power consumption can drop significantly," says Beach.
The new devices with their low power consumption and high switching speed could ultimately be particularly useful for devices such as mobile computing. Strand says, but the work is still at an early stage and will need further development.
"I can see lab prototypes within a few years or less," he says. Making a fully functional memory cell is "quite complex" and can take longer.
The work was supported by the National Science Foundation through the Materials Research Science and Engineering Center (MRSEC) program.