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1. The Best Sandwiches are Not the Most Perfect SandwichesSurprises in the Atomic-Scale Chemical Structure of Next-Generation Magnetic Devices chemical image O, Fe, B structural image • Researchers around the world are trying to develop computer memory that retains information without power — the key to “instant-on” computers. One of the leading contenders for this technology is a type of magnetic “sandwich,” known as a magnetic tunnel junction, made by separating two ultrathin magnets (here, CoFeB) with a few-atoms-thick insulator (here, MgO). • Expecting that the best performance would come from atomically perfect sandwiches, researchers at Cornell developed a new technology to image the atomic-scale chemical structure of the sandwiches. Somewhat surprisingly, they found that the best devices were not perfect. Instead, the best devices were those in which some boron atoms escaped the magnets and crept into the insulator. (In the image at right, the mixture of green boron and red oxygen in the insulator leads to yellow patches in the center of the sandwich.) This surprising discovery points the way to the design of high-performance magnetic memory. Ta CoFeB MgO CoFeB IrMn Left: Electron-microscope image of the layers of a magnetic tunnel junction. The light region in the center is the insulator in the middle of the sandwich. Right: Chemical map of the same junction, in a red-green-blue format displaying the distributions of oxygen (O, red), iron (Fe, blue), and boron (B, green). In this color scheme, red + green = yellow. Therefore, yellow regions in the center of the sandwich indicate an intermixing of oxygen and boron. J. J. Cha, J. C. Read, W. F. Egelhoff, P. Y. Huang,H. W. Tseng, Y. Li, R. A. Buhrman, and D. A. Muller, Applied Physics Letters, 95, 032506 (2009). DMR 0520404 For more details, visit the Cornell Center for Materials Research at www.ccmr.cornell.edu