46 | New Scientist | 30 November 2019
In some ways, though, computer memory
turned out to be the low-hanging fruit. In the
past few years, researchers have realised that
these materials have so much more to offer,
including in endeavours as diverse as medicine
and cosmology (see “Heroic multiferroics”,
page 43). “The applications have exploded
beyond what we ever imagined,” says Spaldin.
In fact, she notes that perhaps the biggest
surprise to emerge from the past two decades
is how many uses have been found for
multiferroic materials that have nothing to
do with the coupling of magnetic and electric
behaviours. “In many applications, we’re
finding that the multiferroicity itself isn’t
as interesting as something else that came
along with it,” says Fiebig. For example, many
multiferroics have a structure that makes
them exceptional harvesters of solar energy.
In principle at least, that means they should
have conversion rates far greater than today’s
silicon-based top performers.
Better and more efficient multiferroics
are surely still out there. And, no doubt,
somewhere beyond them are entirely
new classes of material with as-yet-
undreamed-of combinations of natural
properties. Perhaps all it will take for us to
root them out is for someone like Spaldin
to start asking the right questions. ❚wiggling electrons in the iron ions supply the
magnetic boost. But it isn’t enough to simply
have these two on their own, says Ramesh.
The oxygen atoms play a crucial role too,
creating the stable geometry that allows both
properties to emerge. “You have to have all of
them together in a certain way,” he says.When a plan comes together
In 2003, Spaldin and Ramesh reported on
their first observation of multiferroicity in this
substance. For the first time in history they had
an example of this material that lent itself to
applications. It had the necessary superpowers
and it maintained its properties at room
temperature. The group also showed that it was
ideally suited to uses in computing, especially
memory (see “Boosting memory”, left).
The revelation that practical multiferroics
existed sparked a revolution. Before
2003, the related terms “multiferroic” or
“electro-ferromagnetic” were mentioned in
a few hundred papers. Since 2003, they have
shown up more than 32,000 times. The field
exploded beyond the reach of Spaldin, as labs
around the world took up the challenge to
make and explore their own multiferroics.
“It was exactly like a Bollywood movie,
with a lot of fight scenes, and people crying,
and dance sequences, things like that, but
translated into physics,” jokes Ramesh. Since
then, he and Spaldin and other physicists have
been locked in an ongoing race to extract the
next surprising, serendipitous revelation from
a class of materials that just keeps on giving.Stephen Ornes is a journalist
based in Tennessee. He
tweets @stephenornesGoing beyond the
ferromagnetism
of ordinary bar
magnets was seen
as impossibleBOOSTING
MEMORYComputer hard drives are
essentially made of tiny
magnets whose polarity
can be used to store binary
information. Magnets point one
way for a “1” or flipped over
for a “0”. Right now, computers
use an electric current, applied
directly through a wire, to flip
the magnets when necessary.
Multiferroics suggest
another way. Earlier this year,
Ramamoorthy Ramesh’s group
at the University of California,
Berkeley, unveiled a multiferroic
electrical component that also
stores information as 0s and 1s.
But unlike ordinary hardware,
it doesn’t need current from
a wire. Instead, these switches
can be flipped by applying an
external electric field. That
may not seem like a big deal,
until you consider it would take
10 to 30 times less energy per
bit of information stored to do
it this way.
Given the explosive growth
of power-hungry technologies
like the internet of things,
self-driving cars and artificial
intelligence, it is small wonder
that companies like Intel are
actively pursuing such devices.POWER^ ANDSYRE
D/SCIENCE^ PHOTOLIBRARY4