Apr 14 2015
The researchers fabricated the spintronics devices at the Nano fabrication laboratory at Chalmers University of Technology. From left: Saroj Prasad Dash, Venkata Kamalakar Mutta and André Dankert.
A group of scientists at Chalmers University of Technology has performed an experiment which showed that large area graphene can effectively maintain the electron spin for a long period of time and at the same time it also communicates the spin over longer distances than has been feasible until now.
This latest discovery paves the way for developing spintronic devices, which could make computer processors considerably faster and with higher energy efficiency than they are today.
A quantum mechanical characteristic of basic particles, spin can be directed both up and down and can promote magnetism. For electrons existing in a standard electric current, the spin is distributed in a haphazard manner. However, by using magnets, the electrons can be polarized and fed into a conductor.
Nonetheless, a number of environmental factors can disturb the electron spin. In the conductive material, atoms as well as their crystal structures exhibit an electric field, which is regarded as a magnetic field by the passing electrons. However, this magnetic interference will be restricted because only six protons are present in the carbon atom and these are organized in a symmetrical hexagonal fashion.
Another possible source of interference is the internal spin present in an atomic nucleus. However, this net spin in the nucleus is very small, because most of the carbon atoms contain the C12 isotope with equal number of protons and neutrons.
Built on the electrons’ quantum state, spintronics is being utilized in next-generation hard drives to provide a number of functions such as magnetic random access memory and data storage.
However, in this case, the spin-based data had to shift just a few nanometers and this proves advantageous, because spin is an intrinsic property of electrons which is delicate and does not last long in a large number of materials. Rather than exploiting the electric charges as an information carrier, the electron spin can be leveraged to achieve the same effect.
We believe that these results will attract a lot of attention in the research community and put graphene on the map for applications in spintronic components, said Saroj Dash, who heads the research team at Chalmers University of Technology.
The use of graphene in the electronics industry can positively extend the use of spintronics in this field. This is because graphene is a thin carbon film, which has excellent electrical conducting properties. At the theoretical level, this material is capable of maintaining the electrons without affecting the spin. At present, a number of companies are producing this material through a combination of different techniques, which are all in the initial stage of development.
Graphene was first produced from graphite by means of a standard household tape. This feat was achieved by Nobel Laureates Novoselov and Geim. Today, similar techniques are being utilized to create graphene of high quality. However, the pieces thus obtained are very small.
Scientists at Swedish Linköping University have established the Graphensic company that produces large area graphene grown from a silicon carbide substrate. The Chalmers University of Technology produces large area graphene by utilizing the chemical vapour deposition or CVD technique.
In future spin-based components, it is expected that the electrons must be able to travel several tens of micrometers with their spins kept aligned. Metals, such as aluminium or copper, do not have the capacity to handle this. Graphene appears to be the only possible material at the moment, said Saroj Dash.
Based on information from the electronics industry, it is possible to obtain high-quality graphene in small pieces, but production of larger area graphene can result in low quality and may even include other disadvantages.
The latest study performed by the Chalmers researchers now questions this standard assumption. For the experiment, the researchers procured a CVD graphene from a Spanish-based company, Graphenea. This CVD process imparts roughness, wrinkles, and other defects on the graphene.
However, this method also offers a number of benefits. For instance, it is possible to produce large area graphene at the commercial level, and it is also possible to remove the CVD graphene from the copper foil on which it is grown and can later be placed on a silicon wafer.
While a perfect material could not be obtained, the researchers were able to demonstrate spin parameters, which were considerably higher than those obtained for the CVD graphene on a comparable substrate in the past.
Our measurements show that the spin signal is preserved in graphene channels that are up to 16 micrometers long. The duration over which the spins stay aligned has been measured to be over a nanosecond. This is promising because it suggests that the spin parameters can be further improved as we develop the method of manufacturing, stated Chalmers researcher Venkata Kamalakar, who is also the first author of the study.
The aim of this study is to find a novel way for storing data and carrying out logical operations and is not just relegated to the concept of transferring data in a new material or using graphene in the place of semiconductors or metals. If this idea proves successful, digital technology would soon become a reality. The research team intends to build a logical component, which will include magnetic materials and graphene.
Graphene is a good conductor and has no band gaps. But in spintronics there is no need for band gaps to switch between on and off, one and zero. This is controlled instead by the electron's up or down spin orientations, explained Saroj Dash.
However, more research is needed to establish whether spintronics can substitute semiconductor technology in the near future. Here, graphene offers a promising solution, thanks to its exceptional spin conduction abilities. The research team at Chalmers University of Technology includes Saroj Dash, Venkata Kamalakar, Christiaan Groenveld, and André Dankert. Chalmers' Area of Advance Nanoscience and Nanotechnology has funded the study.
The study has appeared in the journal Nature Communications.