Scientists have taken an important step forward in developing a new material using a honeycomb mesh of nano-sized magnets that could ultimately lead to new types of electronic devices, with greater processing capacity than is currently feasible, in a study published today in the journal Science. Image: Will Branford, Imperial College London |
Scientists
have taken an important step forward in developing a new material using
nano-sized magnets that could ultimately lead to new types of
electronic devices, with greater capacity than is currently feasible, in
a study published today in the journal Science.
Many
modern data storage devices, like hard disk drives, rely on the ability
to manipulate the properties of tiny individual magnetic sections, but
their overall design is limited by the way these magnetic ‘domains’
interact when they are close together.
Now,
researchers from Imperial College London have demonstrated that a
honeycomb pattern of nano-sized magnets, in a material known as spin
ice, introduces competition between neighboring magnets, and reduces
the problems caused by these interactions by two-thirds. They have shown
that large arrays of these nano-magnets can be used to store computable
information. The arrays can then be read by measuring their electrical
resistance.
The
scientists have so far been able to ‘read’ and ‘write’ patterns in the
magnetic fields, and a key challenge now is to develop a way to utilize
these patterns to perform calculations, and to do so at room
temperature. At the moment, they are working with the magnets at
temperatures below -223 C.
Research
author Dr Will Branford and his team have been investigating how to
manipulate the magnetic state of nano-structured spin ices using a
magnetic field and how to read their state by measuring their electrical
resistance. They found that at low temperatures (below -223 C) the
magnetic bits act in a collective manner and arrange themselves into
patterns. This changes their resistance to an electrical current so that
if one is passed through the material, this produces a characteristic
measurement that the scientists can identify.
The
scientists have so far been able to ‘read’ and ‘write’ patterns at room
temperature. However, at the moment the collective behaviour is only
seen at temperatures below minus 223 C. A key challenge now is to
develop a way to utilize these patterns to perform calculations, and to
do so at room temperature.
Current
technology uses one magnetic domain to store a single bit of
information. The new finding suggests that a cluster of many domains
could be used to solve a complex computational problem in a single
calculation. Computation of this type is known as a neural network, and
is more similar to how our brains work than to the way in which
traditional computers process information.
Branford,
who is an EPSRC Career Acceleration Fellow in the Department of Physics
at Imperial College London, said: “Electronics manufacturers are trying
all the time to squeeze more data into the same devices, or the same
data into a tinier space for handheld devices like smart phones and
mobile computers. However, the innate interaction between magnets has so
far limited what they can do. In some new types of memory,
manufacturers try to avoid the limitations of magnetism by avoiding
using magnets altogether, using things like ferroelectric (flash)
memory, memristors or antiferromagnets instead. However, these solutions
are slow, expensive or hard to read out. Our philosophy is to harness
the magnetic interactions, making them work in our favor.”
Although
today’s research represents a key step forward, the researchers say
there are many hurdles to overcome before scientists will be able to
create prototype devices based on this technique such as developing an
algorithm to control the computation. The nature of this algorithm will
determine whether the room temperature state can be used or if the low
temperature collective behaviour is required. However, they are
optimistic that if these challenges can be tackled successfully, new
technology using magnetic honeycombs might be available in ten to
fifteen years.
In
experiments, Branford applied an electrical current across a continuous
honeycomb mesh, made from cobalt magnetic bars each 1 ?m2 long and 100
nm wide, and covering an area 100 ?m2 (as pictured). A single unit
of the honeycomb mesh is like three bar magnets meeting in the centre
of a triangle. There is no way to arrange them without having either two
north poles or two south poles touching and repelling each other, this
is called a ‘frustrated’ magnetic system. In a single triangular unit
there are six ways to arrange the magnets such that they have exactly
the same level of frustration, and as you increase the number of
triangular units in the honeycomb, the number of possible arrangements
of magnets increases exponentially, increasing the complexity of
possible patterns.
Previous
studies have shown that external magnetic fields can cause the magnetic
domain of each bar to change state. This in turn affects the
interaction between that bar and its two neighboring bars in the
honeycomb, and it is this pattern of magnetic states that Dr Branford
says could be computer data.
“The
strong interaction between neighboring magnets allows us to subtly
affect how the patterns form across the honeycomb,” says Branford. “This
is something we can take advantage of to compute complex problems
because many different outcomes are possible, and we can differentiate
between them electronically. Our next big challenge is to make an array
of nano-magnets that can be ‘programmed’ without using external magnetic
fields.”