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Posted: Jan 20, 2012

Buckyballs for next-generation spintronics devices

(Nanowerk News) The beauty of an electron's spin is that it responds very rapidly to small magnetic fields. Such external magnetic fields can be used to reverse the direction of spin. In this way, information can be carried by a flow of electrons. For instance, electrons with a left-hand spin could represent a "1", and those with a right-hand spin, a "0". It takes less time to flip the spin direction than it does to switch a current on or off. Accordingly, spintronics could potentially be very fast and extremely compact.
Organic materials
However, this would require a material that combines the characteristics of a semiconductor (such as silicon, the most widely used material in the chip industry) with magnetic properties. Research in this area (including work by Michel de Jong) has already delivered results. However, finding materials with this combination of properties is far from simple. For this reason, Michel de Jong is now hunting for an alternative. He is focusing on semiconductors consisting of carbohydrate chains, in other words, organic materials. "Such materials are already being used in the displays of the latest smart phones. Indeed, they are very much the 'in' thing. I expect it will ultimately be possible to make very cheap electronics from these materials, leading to a wide range of new applications. For instance, if supermarkets want to tag their products with pricing information, then the electronics involved will have to cost next to nothing."
Bucky balls sandwiched between two ferromagnetic layers, showing the 'spin valve' effect
Bucky balls (C60) sandwiched between two ferromagnetic layers, showing the 'spin valve' effect
De Jong has been experimenting with buckyballs (spherical C60 molecules held together by weak bonds) sandwiched between two magnetic materials. "The great advantage of these molecules is that they have very little effect on electron spin. This enables them to store spin information for much longer periods of time than silicon." Depending on the orientation of the magnetic field in the upper and lower layers of magnetic material, electrons with the same direction of spin are either allowed through or held back, as if a valve were being opened or closed. This would make it possible to create sensitive magnetic sensors, for example. The "sandwich" might also form the basis for new electronic components that make use of spin.
"If we are to make truly effective components, we will need a detailed understanding of events at the interface between the magnetic and organic materials. However, this will require improvements in the quality of such interfaces. The current techniques for applying metallic layers to organic layers do not produce good interconnections. The organic material contains cavities that can fill with metal. This results in unpredictable behaviour. Over the next five years we will be seeking to improve the manufacturing process. This will help us to understand what exactly happens at the interface. I propose to use part of the ERC Grant for this purpose. It will enable me to take on two PhD students and a postdoctoral researcher."
Hysteresis loop for a bucky ball 'sandwich'
Hysteresis loop for the bucky ball 'sandwich', showing low resistance when the spin of the electrons points in the same direction as the magnetic orientation of the ferromagnetic layer (valve effect).
This is the second major ERC Grant to be awarded to Prof. Wilfred van der Wiel's group NanoElectronics, part of the MESA+ Institute for Nanotechnology of the University of Twente. The professor himself obtained a similar European grant in 2009.
Source: University of Twente
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