a constantly growing flood of information, we are being inundated with
increasing quantities of data, which we in turn want to process faster
than ever. Oddly, the physical limit to the recording speed of magnetic
storage media has remained largely unresearched. In experiments
performed on the particle accelerator BESSY II of Helmholtz-Zentrum
Berlin, Dutch researchers have now achieved ultrafast magnetic reversal
and discovered a surprising phenomenon.
magnetic memory, data is encoded by reversing the magnetization of tiny
points. Such memory works using the so-called magnetic moments of
atoms, which can be in either “parallel” or “antiparallel” alignment in
the storage medium to represent to “0” and “1”.
alignment is determined by a quantum mechanical effect called “exchange
interaction”. This is the strongest and therefore the fastest “force”
in magnetism. It takes less than a hundred femtoseconds to restore
magnetic order if it has been disturbed. One femtosecond is a millionth
of a billionth of a second. Ilie Radu and his colleagues have now
studied the hitherto unknown behaviour of magnetic alignment before the
exchange interaction kicks in. Together with researchers from Berlin and
York, they have published their results in Nature.
their experiment, the researchers needed an ultra-short laser pulse to
heat the material and thus induce magnetic reversal. They also needed an
equally short x-ray pulse to observe how the magnetization changed.
This unique combination of a femtosecond laser and circular polarized,
femtosecond x-ray light is available in one place in the world: at the
synchrotron radiation source BESSY II in Berlin, Germany.
their experiment, the scientists studied an alloy of gadolinium, iron
and cobalt (GdFeCo), in which the magnetic moments naturally align
antiparallel. They fired a laser pulse lasting 60 femtoseconds at the
GdFeCo and observed the reversal using the circular-polarized x-ray
light, which also allowed them to distinguish the individual elements.
What they observed came as a complete surprise: The Fe atoms already
reversed their magnetization after 300 femtoseconds while the Gd atoms
required five times as long to do so. That means the atoms were all
briefly in parallel alignment, making the material strongly magnetized.
“This is as strange as finding the north pole of a magnet reversing
slower than the south pole,” says Ilie Radu.
their observation, the researchers have not only proven that magnetic
reversal can take place in femtosecond timeframes, they have also
derived a concrete technical application from it: “Translated to
magnetic data storage, this would signify a read/write rate in the
terahertz range. That would be around 1,000 times faster than
present-day commercial computers,” says Radu.