Wednesday, August 20, 2008

Spintronics Goes Organic

Measuring spin in an organic LED is an important step toward a spintronic device.

By Prachi Patel-Predd

In a spin: Physicists Christoph Boehme (right) and John Lupton have found a way to control an electric current in an organic LED by changing the spin state of electrons in the material. This is a first step toward small, fast spintronic devices made from organic semiconductors. Credit: University of Utah

In electronic circuits, transistors and memory devices process and store an electron's charge. Manipulating another property of electrons, the quantum-mechanical phenomenon known as spin, could lead to faster, smaller, and more energy-efficient computers. University of Utah researchers have now taken a first step toward "spintronic" devices made from organic materials, which should be cheaper and easier to make than with materials used so far.

In a paper published in Nature Materials, the researchers outline a novel experiment that allowed them to measure the electron spins in an organic light-emitting diode (OLED). Using a magnetic field, they were able to control the material's spin state, which also changed the electric current coming out of the device.

A practical spintronic device would have to use electric current to control and read spins. Even though the Utah researchers used a magnetic field to control the spin, their work demonstrates the possibility of spintronics in organic semiconductors, says Johan van Tol, who does spintronic research at the National High Magnetic Field Laboratory in Tallahassee, FL. "Manipulating spin has been done in other materials, but not in these kind of polymers," he says.

Spintronic devices are most easily made from magnetic metals, and researchers have also reported advances in making them from conventional inorganic semiconductors such as silicon and gallium arsenide. But using organic semiconductors could have big advantages. "[Organic devices] are easy to make, easy to deposit and structure; it's all very cheap," says Christoph Boehme, an assistant professor of physics at Utah and a coauthor of the new paper. "You can deposit them on a flexible substrate, and you can deposit them with ink-jet printing."

Electron spin can take on one of two directions: up and down. In conventional electronic circuits, current flowing through a transistor represents a bit with a value of 1, while absence of current signifies a bit with a value of 0. In a spintronic device, 1 and 0 are represented by an up or down spin.