"From a dream with atoms and spins and electrons dancing around, to a device that we use in our daily life” is how Albert Fert described the link between fundamental physics and its applications. His talk during the Tuesday morning session at Lindau focused on how fundamental research could be spun off into new electronic devices.
It can seem inevitable that electronic devices get smaller and smaller over time. But if it weren’t for spin electronics, or spintronics, this trend might not be able to continue much longer into the future. Spintronics uses a property of electrons known as spin, which Fert describes as “a small magnet carried by the electrons”, rather than just electrical charge.
Fert won his Nobel prize for the discovery of Giant Magnetoresistance in 2007 (the discovery was made in 1988, and his prize is shared with Peter Grünberg who independently discovered it at the same time). Giant magnetoresistance uses quantum mechanics to make hard drives and their readers much smaller, packing more information into a smaller space.
The working memory of a computer is known as random access memory, or RAM. During his talk Fert told us about Magnetic RAM, or MRAM. MRAM is an application of spintronics that is useful if you want to send a computer into space or high up in the atmosphere, because it is not damaged by radiation. Perhaps more importantly, it can store data permanently – as well as being working memory, it can act as permanent memory. So if there’s a power cut and you forgot to save the document you were working on, you’ll have nothing to worry about with MRAM. The next generation known as STT-RAM (where STT stands for spin transfer torque) will use spin alone and could be on the market within one or two years. Fert hopes that its lower power usage “will be small contribution to reducing energy use in our society”.
The day before Fert’s session at Lindau, the tables were turned and instead of the Nobel laureates lecturing young researchers, some young researchers got to present their work to a Nobel laureate instead. These master class sessions are much smaller than the plenary lectures, with only a small group of invited young researchers.
At Fert’s masterclass on Monday afternoon, two of the young researchers at the Lindau meeting presented their work in spintronics. First was Karin Everschor who has just finished a PhD at the University of Cologne. She presented a talk on a “mathematical object” known as a skyrmion. Skyrmion’s are named after Tony Skyrme, who developed them to solve a problem in particle physics – but his concept is also useful in spintronics.
To imagine a skyrmion, said Everschor, think of the spikes on a hedgehog, imagine bending the spikes around their centre by applying a magnetic field, then project that onto a flat surface. That’s what a skyrmion looks like. Everschor’s PhD thesis looked at how electrical currents manipulate magnetic structures, like skyrmions.
While Everschor did not go into the details of applications, Fert pointed out after the presentation that skyrmions may be able to provide us with even smaller storage devices. Each skyrmion would be equivalent to a bit, and its spin (up or down) or presence (there or not) would provide the zeros and ones needed to store information. “It’s difficult to compete with size of skyrmions,” said Fert.
The second presentation was from Andrew DiLullo from Ohio University. He presented his work on molecular spintronics. DiLullo’s work involved forming chains of molecules and studying them under a scanning tunnelling microscope. Each molecule has a cobalt centre that provides the spin. The molecules organise themselves into self-assembled chains, each a few nanometers long. In the future, molecular spintronics may be able to provide us with microelectronics much smaller than today’s devices formed from molecules like these.