The application of 'displaced vortex states'
- small magnetic circular movements of just a few
thousandths of a millimetre - may accelerate the
arrival of a new type of magnetic memory (MRAM)
that does not disappear when a computer is switched
off
A
team of scientists from the Universitat Autònoma
de Barcelona, in collaboration with colleagues
from the Argonne National Laboratory (USA) and
the Spintec laboratory (Grenoble, France), has
for the first time produced microscopic magnetic
states, known as "displaced vortex states", that
will allow an increase in the size of MRAMs (which
are not deleted when the computer is switched off).
The research has been published in Physical Review
Letters and Applied Physics Letters.
In
the near future we will turn our computers on
and they will be ready to work almost instantaneously;
no longer will we have to wait a while for the
operating system and certain programs to load into
the RAM. At the moment, SRAM and DRAM do not allow
this, as they are quick, but they are deleted when
the computer is switched off (that is, they are "volatile");
Flash memories, which we use for digital cameras,
are not deleted, but they are slow; MRAM, which
is still being developed, is fast and non-volatile,
but has a relatively low storage capacity. A team
of scientists from the UAB Department of Physics,
in collaboration with colleagues from the Argonne
National Laboratory (USA) and the Spintec laboratory
(Grenoble, France), have discovered a magnetic
phenomenon that could be useful in the quest for
the ideal type of memory: an MRAM with large storage
capacity.
The "displaced vortex states", first observed
by UAB researchers, are small circular movements
of just a few thousandths of a millimetre that
form in the tiny zones where the data is stored.
The information on hard drives has normally been
saved by orientating these zones in specific directions.
The zones pointing upwards, for example, codify
a 1, and those pointing downwards a 0. The smaller
and more compact these zones are, the greater the
capacity of the hard drive. But if they are too
close together, the magnetic field created by one
can affect the neighbouring zone and wipe the data.
However, if the field is saved in a whirlpool form,
in "vortex state", it does not leave the tiny zone
to which it is confined and does not affect the
neighbouring data, thus making it possible for
a much larger hard drive capacity.
The
scientists have achieved these "vortex states" on
small, circular structures that are smaller than
a micrometre (a thousandth of a millimetre) and
combine layers of material with opposing magnetic
properties: a layer of ferromagnetic material and
a layer of antiferromagnetic material. What makes
the configuration of the magnets observed by the
UAB scientists new is that the vortex states are "displaced",
that is, once the magnetic field is no longer applied,
the eye of the whirpool moves off-centre with regard
to the circular structure on which it formed. This
seemingly insignificant detail is the key to applying
the technique to increasing the capacity not only
of hard drives but also Magnetic Random Access
Memories (MRAMs) that are fast, non-volatile, but
until now with small storage capacity.
"The phenomenon observed could also be applied
to other fields, such as improving the read heads
of hard drives", according to Jordi Sort, a UAB-ICREA
physicist and the coordinator of the research. "But
the reason that motivated us is even more fundamental:
this is a very peculiar physical state that can
be observed only in extremely small magnetic structures."
Josep
Nogués (ICREA researcher) and Maria
Dolors Baró, of the UAB Department of Physics,
also took part in the research, which was recently
published in Physical Review Letters and Applied
Physics Letters.
