Energy-efficient transport from magnetic bits made possible
Researchers from Eindhoven University of Technology and the FOM Foundation have succeeded in using electric fields to control the very energy-efficient movement of magnetic domain walls. The discovery is vitally important for the development of the racetrack memory, a highly promising new technology for data storage. PhD researcher Sjors Schellekens and his colleagues from the Physics of Nanostructures group led by Prof.dr. Bert Koopmans published this result on 22 May online in Nature Communications.
The development of traditional electrical memory chips will soon reach its limits. This is because each bit is unavoidably connected to a relatively large and expensive transistor. In magnetic storage, just like on a hard disk, that is not the case. However a hard disk is far too slow to replace the memory chip and its moving parts make it vulnerable. Therefore in 2002, the concept of racetrack memories was devised in which you should be able to store far more data than is the case for current chips. In this memory the magnetic bits – ultra small areas with a different orientation of the magnetization – flow back and forth along a nanowire past the reading and writing head. All of the parts stand still and only the data moves. A crucial aspect of this is managing the 'walls' that border the magnetic bits: if one wall moves faster than the other then they overtake each other and data is lost.
Up until now the speed of the walls could only be controlled using magnetic fields and currents, which is not energy efficient. The assumption was that this could not be done with electrical fields, as these only penetrate the outermost layer of the magnetic storage material. The researchers from Eindhoven circumvented this problem by using an ultrathin film of only several atoms thick. The material therefore largely consists of an 'outermost layer' where the electrical fields penetrate far enough. With this approach the researchers managed to change the speed of the walls by more than a factor of ten. "And our calculations reveal that the effect can become many times greater", says Schellekens.
A major advantage of the electrical fields is the minimum use of energy, so a very small electric current suffices. This means that data can be made available at locations where that is currently not possible. Examples are compact autonomous electronics in the human body or clothing, says Koopmans. In the short term he expects the discovery will lead to a flood of new research to improve the effect and to discover new possibilities. He expects the first applications within ten years.
Reference
'Electric-field control of domain wall motion in perpendicularly magnetized materials' by A.J. Schellekens , A. v.d. Brink, J.H. Franken, H.J.M. Swagten and B. Koopmans (all from Eindhoven University of Technology), Nature Communications. doi: 10.1038/ncomms1848.