Researchers from Institute of Physics AS CR demonstrate a new principle for magnetic recording
Current technologies for writing, storing, and reading information are either charge-based or spin-based. Semiconductor flash or random access memories are prime examples among the large variety of charge-based devices. They utilize the possibility offered by semiconductors to easily electrically manipulate and detect their electronic charge states representing the “zeros” and “ones”. The downside is that weak perturbations such as impurities, temperature change, or radiation can lead to uncontrolled charge redistributions and, as a consequence, to data loss.
Spin-based devices operate on an entirely distinct principle. In some materials, like iron,
electron spins generate magnetism and the position of the north and south pole of the magnet can be
used to store the zeros and ones. This technology is behind memory applications ranging from
kilobyte magnetic stripe cards to terabyte computer hard disks. Since based on spin, the devices
are much more robust against charge perturbations. However, the drawback of current magnetic
memories is that in order to reverse the north and south poles of the magnet, i.e. flip the zero to
one or vice versa, the magnetic bit has to be coupled to an electro-magnet or to another permanent
magnet. If instead one could flip the poles by an electric field without involving another magnet,
a new generation of memories can be envisaged combining the merits of both charge and spin-based
devices.
Researchers from the Institute of Physics of the Academy of Sciences in Prague, in
collaboration with researchers from Cambridge, Nottingham, and Mainz, have discovered a new
physical phenomenon that allows to manipulate the state of a magnet by electric fields.
The work has been published in the journal
Nature Nanotechnology on 2nd March, 2014 (DOI:
10.1038/nnano.2014.15).
In order the shake a magnet electrically without involving an electro-magnet or another
permanent magnet one has to step out of the realm of classical physics and enter the relativistic
quantum mechanics. Einstein’s relativity allows electrons accelerated in an electric field to order
their spins, in other words, to become magnetic. The researchers took a permanent magnet GaMnAs and
accelerated some of the electrons inside the permanent magnet by electric field. These accelerated
electrons created a new internal magnetic cloud which was able to shake the surrounding permanent
magnet, and the researchers detected that the poles of the permanent magnet moved.
The observed phenomenon is closely related to the relativistic spin Hall effect which the
Prague-Cambridge group discovered in 2004 and which since then has become a text-book demonstration
how electrically accelerated electrons can magnetize any material, including common semiconductors.
“Ten years ago we tried to combine the merits of charge and spin-based devices by turning
semiconductors into magnets through the spin Hall effect and now analogous physical phenomenon
allows us to also inverse the approach. We start from a magnet and make it sensitive to electric
fields. Both approaches are promising for realizing a new generation of memories and it is exciting
to be part of the world-wide research and development in this modern field of physics and
microelectronic”, says Tomas Jungwirth from the Prague Institute of Physics.
For detail information contact Tomas Jungwirth from the Institute of Physics AVCR, v.v.i.,
Cukrovarnická 10, 162 53 Praha 6, e-mail:
jungw@fzu.cz
4 Mar 2014
