A new approach to controlling magnetism in a microchip can open the doors to memory, computation and sensing devices that consume drastically less power than existing versions. The approach could also overcome some of the inherent physical constraints that have slowed progress in this area so far.
Researchers at MIT and Brookhaven National Laboratory have shown that they can control the magnetic properties of a thin film material simply by applying a small amount of stress. Changes in magnetic orientation made in this way remain in their new state without the need for any ongoing power, unlike today's standard memory chips, the team has found.
The new discovery is reported today in the newspaper natural materials, in a paper by Geoffrey Beach, a professor of Materials Science and Technology and Co-Chair of the MIT Materials Research Laboratory; PhD student Aik Jun Tan; and eight others at MIT and Brookhaven.
Since silicon microchips approach the basic physical limits that can attract their ability to continue increasing their potential while reducing their power consumption, researchers have investigated a number of new technologies that can come around these limits. One of the promising alternatives is an approach called spintronics, which uses a feature of electrons called spin, instead of its electrical charge.
Since spintronic devices can maintain their magnetic properties without the need for constant power, which silicon chips require, they need significantly less power consumption. They also generate much less heat – another major limiting factor for today's devices.
But spintronic technology suffers from its own limitations. One of the biggest missing ingredients has been a way to quickly and quickly control an electromagnetic properties by applying a voltage. Many research groups around the world have driven that challenge.
Earlier experiments have called for electron accumulation at the interface between a metal 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 with a very small amount, which makes it impractical to use in real devices. It has also tried to use ions instead of electrons to change magnetic properties. For example, oxygenations have been used to oxidize a thin layer of magnetic material, causing extremely large changes in magnetic properties. However, the introduction and removal of oxygen ions causes the material to swell and shrink, causing mechanical damage which limits the process to a few repetitions, making it substantially worthless for computation units.
The new result shows a way around it, using hydrogen ions instead of the much larger surges used in previous trials. Because the hydrogen ions can zip in and out very easily, the new system is much faster and provides other significant benefits, researchers say.
Because the hydrogen ions are so much smaller, they can come in and out of the crystalline structure of the Spintronican system, change their magnetic orientation each time without damaging the material. In fact, the team has now shown that the process does not produce any decomposition of the material after more than 2000 cycles. And unlike oxygenations, hydrogen can easily pass through metal layers, allowing the layer to control properties of layers deep in a device that can not be controlled in any other way.
"When you pump hydrogen to the magnet, magnetization rotates," says Tan. "You can actually shift the 90 degree magnetization direction by applying a voltage – and it's completely reversible." Because the magnetic poles orientation is what is used to store information, it means that it is possible to easily write and delete data "bits" in spintronic devices with this effect.
Beach, whose laboratory discovered the original process of controlling magnetism through oxygenations several years ago, said that the first discovery released widespread research on a new area called "magnetic jonics" and now has this newest battle "ending in the whole this area. "
"This is really an important breakthrough," said Chris Leighton, professor of Distinguished McKnight University at the Department of Chemical Engineering and Materials Science at the University of Minnesota, who was not involved in this work. "There is currently a great interest around the world to control magnetic materials simply by using electrical voltages. It's not only interesting from the ground, but it's also a potential game switch for applications where magnetic materials are used to store and process digital information. "
Leighton says that "The use of hydrogen input to control magnetism is not new, but it can be done in a power-driven manner, in a solid state device with a good impact on magnetic properties – it's quite important!" He adds, "This is something new, with the potential to open further new research areas. At the end of the day, it's quite exciting to control any kind of material by literally turning the switch. To be able to do it fast enough, Over enough bikes, in a general way, would be a great step for science and technology. "
In essence, Beach tells him and his team "trying to make a magnetic analogue of a transistor" that can be turned on and off repeatedly without deteriorating its physical properties.
Just add water
The discovery came in part, through serendipity. Tan found that the results of his experiment varied greatly from day to day for reasons that were not obvious. Eventually, by examining all conditions during the various tests, he realized that the key factor was humidity: the experiment worked better on humid days compared to dry. The reason he eventually realized where the water molecules from the air were divided into oxygen and hydrogen on the charged surface of the material and while the oxygen was released to the air, the hydrogen ion ionized and penetrated the magnet device – and replaced its magnetism.
The unit that the team has produced consists of a sandwich with several thin layers, including a cobalt layer in which the magnetic changes occur, sandwiched between layers of a metal such as palladium or platinum, and with a layer of gadolinium oxide and then a gold layer to connect to the electrical voltage.
Magnetism is switched with just a short application of voltage and then stops. Reverse it requires no power at all, only short circuit of the device to connect its two sides electrically, whereas a conventional memory circuit requires constant power to maintain its state. "Because you're just using a pulse, power consumption can go down," says Beach.
The new devices, with low power consumption and high switching speed, may eventually be particularly useful for devices such as mobile computers, says Beach, but work is still early and will require further development.
"I can see laboratory-based prototypes within a few years or less," he says. Making a full work memory cell is "quite complex" and can take longer, he says.
The work was supported by the National Science Foundation through the Materials Research Science and Engineering Center (MRSEC) Program.