New way to explore and control atom-scale magnetism

IBM researchers built a chain of manganese atoms up from two to 10 atoms in length atop an extremely thin electrically insulating surface. Using their new spin-excitation spectroscopy technique, the IBM researchers measured how the magnetic properties of the chain changed as each new atom was added. They found that chains with an even number of atoms had no net magnetism, while chains with an odd number of atoms showed net magnetism.

The STM detects atoms and surfaces by measuring current tunneling between the microscope tip and the sample surface. The topography seen in the image represent the electron density surrounding each atom. Manganese atoms atop the surface appear as steep hills. Although the image shows the Mn electrons in the chain as a smooth ridge, each atom is separated by 0.36 nm, which is about 50 percent farther apart than they are separated in bulk manganese.

Since much less current flows through the insulating copper nitride areas, it is an artifact of STM imaging that the CuN surface appears to be depressed below the surrounding plain copper metal surface.

The field of view is 7.8 nm wide by 7.8 nm deep. The bump in the left foreground is a single manganese atom.
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STM image of 28nm by 28nm area of the terraced copper and copper nitride surface where the IBM experiments were performed. The smooth flat surfaces are copper metal; the cross-hatched, slightly depressed areas are patches of insulating CuN, which were created by implanting a sub-monolayer amount of nitrogen and heating the surface. The scientists wanted both sufaces close to each other so they could easy test magnanese-atom structures on both the conducting and insulating surfaces. The visible humps on the surfaces are the manganese structures (1-10 atoms long)
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This image shows a calculated cross-section of the CuN surface layer before (top) and after Mn atoms are placed on the surface. (This calculation is not part of the Science Express paper itself; it was done for another paper by colleague Chiung-Yuan Lin.)
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