Magnetic moment of single holmium atoms stabilized by symmetry
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Magnetic moment of single holmium atoms stabilized by symmetry
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ingle or assemblies of magnetic at oms positioned on non-magnetic substrates have great potential in high density magnetic data storage and quantum computing applications. However, they suffer the limitation that the magnetic moments of these atoms are easily destabilized by interactions with the substrate, resulting in very short lifetimes. An international team including researchers from Karlsruhe Institute of Technology (KIT), the Max Planck Institute (MPI) of Microstructure Physics in Halle, the University of Leipzig, Germany, and the University of Tokyo, Japan, have now found a route to overcome this problem, as described in November 14 issue of Nature (DOI:10.1038/nature12759; p. 242). An individual holmium atom was fixed to a metal surface so that the spin of one holmium electron remains stable for more than 10 minutes. The spin can be descriptively understood as a rotation direction of an electron, giving it a magnetic moment that can align itself in a particular direction in an external magnetic field. A network of several hundred million atoms is necessary for a magnetic bit to remain stable enough for hard disk data to remain safe for years.
of the crystals, which determines the final crystal shape. Ratios that do not follow the recipe lead to large fluctuations in energy and result in a sphere, not a faceted crystal, Olvera de la Cruz said. With the correct ratio, the energies fluctuate less and result in a crystal every time. To achieve a self-assembled single crystal, the research team took two sets of gold nanoparticles functionalized with complementary DNA linker strands. Working with approximately 1 million nanoparticles in water, they heated the solution to a temperature just above the DNA linkers’ melting point and then slowly cooled the solution to room temperature, over a period of two to three days.
The very slow cooling process encouraged the single-stranded DNA to find its complement, resulting in a high-quality single crystal approximately 3 μm in size. The researchers determined that the length of DNA connected to each gold nanoparticle cannot be much longer than the size of the nanoparticle. In the study, the gold nanoparticles varied from 5 nm to 20 nm in diameter; for each, the DNA length that led to crystal formation was about 18 base pairs and six single-base “sticky ends.” “There’s no reason we can’t grow extraordinarily large single crystals in the future using modifications of our technique,” said Mirkin.
“One individual atom fixed to a substrate is usually so sensitive that it keeps its magnetic orientation for mere fractions of a microsecond (200 nanoseconds),” said co-author Wulf Wulfhekel from KIT. Their current research, Wulfhekel said, “not only opens the door to denser computer storage devices, but could also lay the foundation for constructing quantum computers.” In their latest experiment, the researchers placed one individual atom of the rare-earth metal holmium onto a platinum substrate. At temperatures
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