A new approach to magnetism control in the microchip could open the door to memory, computer and sensor devices that consume drastically less energy than the existing versions. Access could also overcome some of the inherent physical limitations that have so far slowed progress in this area.
Researchers at MIT and Brookhaven National Laboratory have demonstrated that they can control the magnetic properties of thin film material by simply applying low voltage. Changes in magnetic orientation thus made remain in the new state without the need for any kind of permanent power, unlike today's standard memory chips, the team has found.
A new discovery was published today in the journal Natural materials, in the work of Geoffrey Beach, professor of material sciences and engineering and co-founder of the MIT Materials Research Laboratory; graduate student Aik Jun Tan; and eight others at MIT and Brookhaven.
Since silicon microchips are approaching the underlying physical limitations that could limit their ability to continue to increase their capabilities while simultaneously reducing their energy consumption, researchers explore various new technologies that could overcome these limits. One of the promising alternatives is an approach called Spintronics, which uses the electron-named spin instead of their electrical charge.
Since spintronic devices can retain their magnetic properties without the need for constant power, which requires a silicon memory chip, they need far less power to operate. They also create far less heat – another big limiting factor for today's devices.
But spintronic technology suffers from its own limitations. One of the biggest missing ingredients was the way to manually and quickly manage the magnetic properties of the material electrically, using a voltage. Many research teams around the world are implementing this challenge.
Previous attempts rely on the accumulation of electrons on the interface between metal magnets and isolates, using the structure of a device similar to the condenser. The electric charge can change the magnetic properties of the material, but only a very small amount, which is why it is impractical for use in real-life devices. They also tried to use ion instead of electrons to change magnetic properties. For example, oxygen ions are used to oxidize a thin layer of magnetic material, which causes extremely large changes in magnetic properties. However, inserting and removing the oxygen ion causes the material to crimp and collect, causing mechanical damage that limits the process to just a few repetitions – making it essential for computer devices.
A new discovery shows the way around this, using hydrogen ions instead of the much larger oxygen ions used in previous attempts. Since hydrogen ions can buzz and go out very easily, the new system is much faster and provides other significant benefits, researchers say.
Since the hydrogen ions are so small, they can enter and exit the crystal structure of the spintronic device, changing its magnetic orientation every time without damage to the material. In fact, the team has now shown that this process does not produce material degradation after more than 2000 cycles. And, unlike oxygen ions, hydrogen can easily pass through metal layers, which allows the team to control layer properties deeply in a device that can not otherwise be controlled.
"When you pump hydrogen to the magnet, magnetization turns," Tan says. "You can actually switch the direction of magnetization by 90 degrees using the voltage – and that's completely reversible." Since the magnet pole orientation is what is used to store data, it means it is easy to write and delete "bit" data in spintronic devices using this effect.
The beach, whose laboratory discovered the original process of controlling magnetism over the oxygen ion several years ago, says the initial finding dispersed a broad exploration of the new area called the "magnetic ion", and now this latest finding "turned to the end of this whole field."
"This is really a significant breakthrough," says Chris Leighton, a prominent professor of McKnight at the Department of Chemical Engineering and Materials Science at the University of Minnesota, who was not involved in this paper. "At present, there is a huge interest in controlling magnetic materials by simply applying electrical voltages. It is not only interesting to the core, but also a potential player for applications where magnetic materials are used for storage and processing of digital information."
Leighton says, "The use of hydrogen insertion to control magnetism is not new, but it is able to do it in a rigidly controlled, solid state, with a good influence on magnetic properties – that's quite significant!" Adding, "This is something new, with the ability to open new areas of research … At the end of the day, control of any kind of material works literally flipping switch is pretty exciting. Being able to do it fast enough, enough cycles, in a general way , it would be a fantastic step forward for science and engineering. "
Basically, Beach explains, he and his team are "trying to make a magnetic analog transistor," which can be switched on and off without humiliating its physical properties.
Just Add Water
The discovery came, in part, through seriousness. While experimenting with layered magnetic materials in search of ways of changing their magnetic behavior, Tan found that the results of his experiments were significantly different from day to day for reasons that were not obvious. Finally, examining all the conditions during the various tests, he realized that the main difference was the humidity of the air: The experiment worked better on wet days compared to the dry. The reason was, in the end, that air molecules from the air were divided into oxygen and hydrogen on the charged surface of the material, and as oxygen flushed into the air, hydrogen was ionized and penetrated into a magnetic device – and changed its magnetism.
The device made by the team consists of sandwiches of several thin layers, including a cobalt layer in which magnetic changes take place, arranged between layers of metal such as palladium or platinum and a gadolinium oxide coating, and then the golden layer for connection to the electric drive voltage.
Magnetism is switched only by short voltage, and then remains. Reversing does not require any energy, it only shortens the device to connect its two sides electrically, while the conventional memory chip requires constant power to maintain its status. "Because you're just applying a pulse, energy consumption can go down," says Beach.
New devices, with low power consumption and high switching speeds, could ultimately be particularly useful for devices such as mobile computing, says Beach, but the job is still at an early stage and will require further development.
"I can see lab prototypes within a few years or less," he says. Making full memory is "fairly complex" and can take longer, he says.
The paper supported the National Foundation for Science through the Science and Engineering Research Program (MRSEC) program.