A breakthrough in the understanding of the magnetic properties of organic semiconductors could lead to cheaper tablet PCs. 

In 2004 a group of researchers from the University of Iowa, US, discovered a strange magnetic effect in films of an organic semiconductor. When a small magnetic field was applied to the film, its electrical resistance decreased by around ten per cent. This unusual sensitivity to magnetic fields is known as magnetoresistance, and had only previously been found in ferromagnetic materials like iron. The cause of the phenomenon was a mystery.

Now the researchers have taken a step forward in understanding why the magnetoresistance happens. By studying films of a variety of organic semiconductors, they have narrowed down the cause to the combined influence that heavy atoms, such as platinum or iridium, and hydrogen atoms have on electrons in the material. On the atomic scale, the electrical and magnetic responses of materials are strongly linked. Both heavy atoms and hydrogen atoms subtly change the energy levels of electrons in the film, and the interplay of the two effects causes strong magnetoresistance. 

Markus Wohlgenannt, who led the research, said, 'what is particularly nice about our discovery is that is has an immediate potential application in organic LED pen-input displays. These interactive displays will have functions similar to existing personal digital assistants and tablet PCs, where a person uses a magnetic pen to input handwritten data or activate desktop icons. The major advantage of our technology compared to existing technologies is that the light-emitting pixels and the magnetic pen sensors are one and the same element, leading to a significant cost reduction.' 

Clare Boothby