Capstone in magnetic hard-disk design
Context: In a hard drive, each bit of information is written on magnetic grains inside a hard disk. Engineers have so far squeezed more data into smaller media by using fewer and fewer grains to hold each bit. But hard-disk manufacturers are now up against physical limits on how much their grains can shrink before they become unstable and lose data. Recent work by researchers from the University of Konstanz in Germany and Hitachi reveals a new magnetic medium that could be the basis for the hard drive of the future.
Methods and Results: Manfred Albrecht and colleagues created their hard-disk medium by first putting down a layer of closely packed nanoscale latex spheres. By sprinkling atoms of cobalt and palladium onto the spheres, they created “magnetic caps” that can store a binary digit as the polarity of a magnetic field. But while its polarity can be flipped, the field always remains perpendicular to the thickest part of the caps. So when the cobalt and palladium rain down onto the spheres from directly above, the magnetic field is perpendicular to the disk surface, as in today’s most advanced hard drives. By orienting the layer of spheres at a 45-degree angle to the stream of cobalt and palladium, the authors created a medium that should be more responsive to magnetic fields from a recording head. This could allow manufacturers to use materials that are magnetically more stable than those in conventional hard drives, enabling more-shrinkable magnetic bits.
Why it Matters: Increases in storage density have enabled hard drives to capture markets in portable electronics such as MP3 players and, more recently, cell phones. Advances like those by Albrecht and colleagues could improve hard-drive capacities another tenfold or more, which would greatly reduce the physical size of current systems and enable, for instance, a new generation of portable video devices.
Source: Albrecht, M., et al. 2005. Magnetic multilayers on nanospheres. Nature Materials 4:203-206.
Thinner, cheaper fuel cell catalysts
Context: Fuel cells are much ballyhooed as the future of energy production. In a fuel cell, hydrogen and oxygen combine to produce electricity and water, but getting them to react in a controllable way requires an expensive platinum catalyst. To make current fuel cell designs economically viable, the amount of platinum used must be reduced by nine-tenths. Now, researchers from Brookhaven National Laboratory and the University of Wisconsin-Madison have shown that using less platinum can lead to a more efficient catalyst. The discovery opens a new route to cheaper, more efficient fuel cells.
Methods and Results: Junliang Zhang and colleagues coated five different metals with a layer of platinum one atom thick and tested them in a model system meant to mimic a fuel cell. In such a system, hydrogen and oxygen gases collect on the metal surface, where they react to form water and release electric current. For most of the platinum “monolayers,” the reaction occurred more slowly than it does on the thicker platinum layer currently used in fuel cells, but adding a monolayer of platinum to palladium sped up the reaction. To explain their experimental results, the authors simulated the system using a technique called density-functional theory. Their computations predicted how the performance of the platinum monolayer would be affected by atoms from the underlying layer of metal. The theory aligned well with their experiments and showed that adding a platinum monolayer to palladium balances two competing needs: it is reactive enough to break the bonds between oxygen atoms yet does not cling to the oxygen atoms so tightly that it prevents them from reacting with hydrogen.
Why it Matters: Because fuel cells are efficient and do not directly generate harmful emissions, many expect them to become a source of power for cars, homes, and even portable electronics like cell phones. If the amount of platinum they require can be reduced to a monolayer, commercial fuel cells could enjoy a quick and broad entry into the market. Tailoring the surfaces of metals to boost their catalytic capacities should also have applications in chemical manufacturing and pollution control. If such applications can be found through theoretical analysis, then cleaner, faster, and more efficient production techniques won’t take such a toll on research and development budgets.
Source: Zhang, J., et al. 2005. Controlling the catalytic activity of platinum monolayer electrocatalysts for oxygen reduction with different substrates. Angewandte Chemie International Edition 44:2132-2135.
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