An upper speed limit for writing magnetic information to a computer鈥檚 hard drive has been discovered by physicists.
In order to work out the speed barrier, the researchers used a 3.2-kilometre-long particle accelerator to fire a tightly packed bunch of electrons at magnetic material. They found that the limit was about 1000 times slower than previously thought, but say there may be ways to get around it in order to make hard drives even more efficient.
Information is stored on a computer鈥檚 hard drive in the form of ones and zeroes. These 鈥渂its鈥� of data are recorded magnetically 鈥� by making the millions of atoms within designated areas spin either up or down using a magnetic field. This information can then be read back from the disk also using a magnetic field.
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The best personal computers can 鈥渇lip鈥� these spins at in a few billionths of a second (nanoseconds). But Joachim St枚r and colleagues at Stanford University in California, US, used the Stanford Linear Accelerator (SLAC) to determine how much faster information could be written magnetically.
Speed of light
The key to increasing the speed of magnetisation is applying a very strong field extremely quickly.
So the team used a beam of tightly-packed electrons travelling close to the speed of light to generate a series of extremely brief magnetic field pulses which they fired at a magnetic target. The pulses lasted just 2.3 trillionths of a second (picoseconds) and measured 10 Tesla, or 200,000 times the strength of the Earth鈥檚 magnetic field.
In photographs of the target material they expected to see dark and light areas corresponding to up and down magnetic spins. But the atoms refused to change their polarity in unison and no coherent pattern was seen.
Precisely why the brief pulses should fail to magnetise the target uniformly remains a mystery. 鈥淲e have a rough idea of the physical principles at work but a quantitative theory does not yet exist,鈥� St枚r told New 杏吧原创. But the researchers best guess is that thermal fluctuations somehow interfere with magnetisation at such high speeds.
Ever smaller
Increasing the amount of information that can be stored on hard drives requires manufacturers to use smaller areas of disk surface, and hence fewer atoms.
But altering ever smaller groups of atoms means using materials that are harder to magnetise, to prevent interference, and that requires a stronger magnetic field and faster application.
So, although the limit discovered by the Stanford team is well beyond the capabilities of current hard drives, it does represent a potential future barrier.
鈥淣o matter how short and strong the magnetic-field pulse, magnetic recording cannot be made ever faster,鈥� says Danilo Pescia at ETH-H枚enggerberf in Zurich, Switzerland. 鈥淭his is because such dangerous 鈥榙eformations鈥� of the spin distribution must be avoided to achieve reliable recording.鈥�
However, St枚r notes that it may yet be possible to get around this stumbling block. This is because magnetisation can also be sped up using heat combined with a magnetic field.