Newly Magnetic Graphene Could Shrink Transistors
CREDIT: University of Manchester
Is there anything that "miracle material" graphene cannot do? Its newly found property, magnetism that can be switched on and off, could pave the way to new transistor-like devices that are much smaller, consume less energy and have greater processing speeds than today's electronics.
Graphene is a two-dimensional layer of carbon atoms arranged in a honeycomb fashion, and it has already been dubbed the strongest, thinnest and most conductive material ever found.
Now, its newly discovered magnetic property could lead to the fabrication of devices based on the principle of spintronics, said Andre Geim of Manchester University in the United Kingdom, a co-author of the recent study. In 2010, Geim shared a Nobel Prize for extracting graphene from graphite, commonly used as lead in pencils, using plain old sticky tape. [Read also: "What is a Transistor?"]
In today's everyday electronics, information is carried by an electric current — a flow of charged particles. But charge is only one property of electrons; they also behave like tiny magnets, and this characteristic is known as spin.
"Usually, in solids, the spins of electrons are pointing in opposite directions and their tiny magnetism does not play any role," said the lead author of the study, Irina Grigorieva of the University of Manchester. "It is possible, however, to create situations where electron spin will be usefully employed, and this is the objective of spintronics. Its great advantage is that, unlike the charge of electrons, their spin is retained when the power is off, which can be used as the basis fo flash-memory like devices."
Spintronics, which essentially means "spin transport electronics," has been an important area of research, and magnetic materials are already used in a number of information-storage devices such as hard disks and memory chips in computers, and magnetic stripes on credit cards.
But all these spintronic devices are "passive," said Geim. Tiny magnets store bits of information (0 or 1) using north or south polarization, but they do not actively flip between their magnetic and non-magnetic states.
Achieving this on-off capability would make it possible to create an active spintronic device, such as a transistor, the basic processing unit of a computer chip. Currently, transistors are made of a semiconductor material called silicon, in which an on-off switch either allows the current to flow through or blocks it. – You can use both semiconductor material and semiconducting material
"Controlling the spin flow is the Holy Grail of spintronics," Geim said. "The current work shows that we can do it, just by applying electric field, which is a principle similar to electronics currently used in computers. But instead of charge flow, we control spin flow."
In 2012, the same team of researchers showed that it was possible to make graphene magnetic, by either removing some carbon atoms from the graphene lattice or by "peppering" graphene with fluorine atoms. To go a step further and switch this magnetism on and off, the scientists decided to "flood" the material with electrons.
To do so, the researchers splashed graphene with a layer of molecules, for example, nitric acid. These molecules provided extra electrons, thus increasing the total number of electrons.
The researchers then measured the amount of magnetism of the material, what is known as its magnetic moment, using a very sensitive magnetometer.
"We found that that the magnetic moment disappeared completely when the amount of electrons was above a certain value but was then switched back on by reducing the amount of electrons inside," said Grigorieva.
The same on-off control can be accomplished by simply applying an electric field, she added, which also floods a material with electrons, and then turning the field off to switch off the magnetism.
Physicist Andrea Ferrari from the University of Cambridge in the United Kingdom, who was not involved in the study, said that the research was "very fundamental" and could help make transistors much smaller than they currently are.
"Controlling spin in graphene by applying an electric field could have direct implications for future spintronic devices, in principle providing a means to beat the current Moore's law," Ferrari said.
Defined by Intel co-founder Gordon Moore in 1965, Moore’s law states that the number of transistors on a computer chip will double roughly every two years, for the same cost, and this can be achieved by making transistors smaller and smaller.
The prediction has held true so far, but there must be a limit; at some point, it won't be possible to shrink a transistor any further.
But active spintronic devices based on graphene may allow the law to hold for a while longer, said Ferrari.
The study was published in the journal Nature Communications.